Preprints (publication date not yet finalized)

Articles published in the last few months, or not previously reported

  • June 2009
Piserchio A, Nair PA, Shuman S, et al. Sequence-specific H-1(N), C-13, and N-15 backbone resonance assignments of the 34 kDa Paramecium bursaria Chlorella virus 1 (PBCV1) DNA ligase. BIOMOLECULAR NMR ASSIGNMENTS 2009 June; 3 (1): 77-80 mskc.gif

Piserchio, A., Ghose, R., Cowburn, D. Optimized bacterial expression and purification of the c-Src catalytic domain for solution NMR studies. J Biomol NMR 2009 Jun; 44 (2):87-93 cuny.gif
Progression of a host of human cancers is associated with elevated levels of expression and catalytic activity of the Src family of tyrosine kinases (SFKs), making them key therapeutic targets. Even with the availability of multiple crystal structures of active and inactive forms of the SFK catalytic domain, a complete understanding of its catalytic regulation is unavailable. Also unavailable are atomic or near-atomic resolution information about their interactions, often weak or transient, with regulating phosphatases and downstream targets. Solution NMR, the biophysical method best suited to tackle this problem, was previously hindered by difficulties in bacterial expression and purification of sufficient quantities of soluble, properly folded protein for economically viable labeling with NMR-active isotopes. Through a choice of optimal constructs, co-expression with chaperones and optimization of the purification protocol, we have achieved the ability to bacterially produce large quantities of the isotopically-labeled catalytic domain of c-Src, the prototypical SFK, and of its activating Tyr-phosphorylated form. All constructs produce excellent spectra allowing solution NMR studies of this family in an efficient manner.

  • May 2009
Chakravarty S, Zeng L, Zhou MM. Structure and Site-Specific Recognition of Histone H3 by the PHD Finger of Human Autoimmune Regulator. Structure 2009 May 13; 17 (5):670-9 mssm.gif
Human autoimmune regulator (AIRE) functions to control thymic expression of tissue-specific antigens via sequence-specific histone H3 recognition by its plant homeodomain (PHD) finger. Mutations in the AIREPHDfinger have been linked to autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED). Here we report the three-dimensional solution structure of the first PHD finger of human AIRE bound to a histone H3 peptide. The structure reveals a detailed network of interactions between the protein and the amino-terminal residues of histone H3, and particularly key electrostatic interactions of a conserved aspartic acid 297 in AIRE with the unmodified lysine 4 of histone H3 (H3K4). NMR binding study with H3 peptides carrying known posttranslational modifications flanking H3K4 confirms that transcriptional regulation by AIRE through its interactions with histone H3 is confined to the first N-terminal eight residues in H3. Our study offers a molecular explanation for the APECED mutations and helps define a subclass of the PHD finger family proteins that recognize histone H3 in a sequence specific manner.

Claudia Bertonati, Marco Punta, Markus Fischer, Guy Yachdav, Farhad Forouhar, Weihong Zhou, Alexander P. Kuzin, Jayaraman Seetharaman, Mariam Abashidze, Theresa A. Ramelot, Michael A. Kennedy, John R. Cort, Adam Belachew, John F. Hunt, Liang Tong, Gaetano T. Montelione, and Burkhard Rost. Structural genomics reveals EVE as a new ASCH/PUA-related domain. Proteins 2009 May 15; 75 (3):760-733 ColumbiaUniversityintheCityofNewYorkcopy.gif
Rutgers U.
We report on several proteins recently solved by structural genomics consortia, in particular by the Northeast Structural Genomics consortium (NESG). The proteins considered in this study differ substantially in their sequences but they share a similar structural core, characterized by a pseudobarrel five-stranded beta sheet. This core corresponds to the PUA domain-like architecture in the SCOP database. By connecting sequence information with structural knowledge, we characterize a new subgroup of these proteins that we propose to be distinctly different from previously described PUA domain-like domains such as PUA proper or ASCH. We refer to these newly defined domains as EVE. Although EVE may have retained the ability of PUA domains to bind RNA, the available experimental and computational data suggests that both the details of its molecular function and its cellular function differ from those of other PUA domain-like domains. This study of EVE and its relatives illustrates how the combination of structure and genomics creates new insights by connecting a cornucopia of structures that map to the same evolutionary potential. Primary sequence information alone would have not been sufficient to reveal these evolutionary links.

Ferrage F., Cowburn D., Ghose R. Accurate Sampling of High-Frequency Motions in Proteins by Steady-State (15)N-{(1)H} Nuclear Overhauser Effect Measurements in the Presence of Cross-Correlated Relaxation. J Am Chem Soc 2009 May 6; 131 (17):6048-9 cuny.gif
The steady-state {(1)H}-(15)N NOE experiment is used in most common NMR analyses of backbone dynamics to accurately ascertain the effects of the fast dynamic modes. We demonstrate here that, in its most common implementation, this experiment generates an incorrect steady state in the presence of CSA/dipole cross-correlated relaxation leading to large errors in the characterization of these high-frequency modes. This affects both the quantitative and qualitative interpretation of (15)N backbone relaxation in dynamic terms. We demonstrate further that minor changes in the experimental implementation effectively remove these errors and allow a more accurate interpretation of protein backbone dynamics.

  • April 2009
Jeong H, Then F, Melia TJ Jr, Mazzulli JR, Cui L, Savas JN, Voisine C, Paganetti P, Tanese N, Hart AC, Yamamoto A, Krainc D. Acetylation targets mutant huntingtin to autophagosomes for degradation. Cell. 2009 Apr 3; 137 (1):60-72 nyu.gif ColumbiaUniversityintheCityofNewYorkcopy.gif
Huntington's disease (HD) is an incurable neurodegenerative disease caused by neuronal accumulation of the mutant protein huntingtin. Improving clearance of the mutant protein is expected to prevent cellular dysfunction and neurodegeneration in HD. We report here that such clearance can be achieved by posttranslational modification of the mutant Huntingtin (Htt) by acetylation at lysine residue 444 (K444). Increased acetylation at K444 facilitates trafficking of mutant Htt into autophagosomes, significantly improves clearance of the mutant protein by macroautophagy, and reverses the toxic effects of mutant huntingtin in primary striatal and cortical neurons and in a transgenic C. elegans model of HD. In contrast, mutant Htt that is rendered resistant to acetylation dramatically accumulates and leads to neurodegeneration in cultured neurons and in mouse brain. These studies identify acetylation as a mechanism for removing accumulated protein in HD, and more broadly for actively targeting proteins for degradation by autophagy.

Ramelot T.A., Raman S., Kuzin A.P., Xiao R., Ma L.C., Acton T.B., Hunt J.F., Montelione G.T., Baker D., Kennedy M.A. Improving NMR protein structure quality by Rosetta refinement: A molecular replacement study. Proteins 2009 Apr; 75 (1):147-67 ColumbiaUniversityintheCityofNewYorkcopy.gif
Rutgers U.
U. Washington
The structure of human protein HSPC034 has been determined by both solution nuclear magnetic resonance (NMR) spectroscopy and X-ray crystallography. Refinement of the NMR structure ensemble, using a Rosetta protocol in the absence of NMR restraints, resulted in significant improvements not only in structure quality, but also in molecular replacement (MR) performance with the raw X-ray diffraction data using MOLREP and Phaser. This method has recently been shown to be generally applicable with improved MR performance demonstrated for eight NMR structures refined using Rosetta (Qian et al., Nature 2007;450:259-264). Additionally, NMR structures of HSPC034 calculated by standard methods that include NMR restraints have improvements in the RMSD to the crystal structure and MR performance in the order DYANA, CYANA, XPLOR-NIH, and CNS with explicit water refinement (CNSw). Further Rosetta refinement of the CNSw structures, perhaps due to more thorough conformational sampling and/or a superior force field, was capable of finding alternative low energy protein conformations that were equally consistent with the NMR data according to the Recall, Precision, and F-measure (RPF) scores. On further examination, the additional MR-performance shortfall for NMR refined structures as compared with the X-ray structure were attributed, in part, to crystal-packing effects, real structural differences, and inferior hydrogen bonding in the NMR structures. A good correlation between a decrease in the number of buried unsatisfied hydrogen-bond donors and improved MR performance demonstrates the importance of hydrogen-bond terms in the force field for improving NMR structures. The superior hydrogen-bond network in Rosetta-refined structures demonstrates that correct identification of hydrogen bonds should be a critical goal of NMR structure refinement. Inclusion of nonbivalent hydrogen bonds identified from Rosetta structures as additional restraints in the structure calculation results in NMR structures with improved MR performance.

  • March 2009
Miloushev V.Z., Levine J.A., Arbing M.A., Hunt J.F., Pitt G.S., Palmer A.G. III. Solution Structure Of The NaV1.2 C-Terminal EF-Hand Domain J Biol Chem 2009 Mar 6; 284 (10):6446-54 ColumbiaUniversityintheCityofNewYorkcopy.gif
Voltage-gated sodium channels initiate the rapid upstroke of action potentials in many excitable tissues. Mutations within intracellular C-terminal sequences of specific channels underlie a diverse set of channelopathies, including cardiac arrhythmias and epilepsy syndromes. The three-dimensional structure of the C-terminal residues 1777-1882 of the human NaV1.2 voltage-gated sodium channel has been determined in solution by NMR spectroscopy at pH 7.4 and 290.5 K. The ordered structure extends from residues Leu 1790 to Glu 1868 and is composed of four α helices separated by two short anti-parallel β-strands; a less well-defined helical region extends from residue Ser 1869 to Arg 1882; and a disordered N-terminal region encompasses residues 1777-1789. Although the structure has the overall architecture of a paired EF-hand domain, the NaV1.2 C-terminal domain does not bind Ca2+ through the canonical EF-hand loops, as evidenced by monitoring 1H-15N chemical shifts during a Ca2+ titration. Backbone chemical shift resonance assignments and Ca2+ titration also were performed for the NaV1.5 (1773-1878) isoform, demonstrating similar secondary structure architecture and absence of Ca2+ binding by the EF-hand loops. Clinically significant mutations identified in the Cterminal region of NaV1 sodium channels cluster in the helix I-IV interface and the helix II-III interhelical segment or in helices III and IV of the NaV1.2 (1777-1882) structure.

  • February 2009
Matthew J. Bick, Valerie Lamour, Kanagalaghatta R. Rajashankar,Yuliya Gordiyenko, Carol V. Robinson, and Seth A. Darst. How to Switch Off a Histidine Kinase: Crystal Structure of Geobacillus stearothermophilus KinB with the inhibitor Sda. J Mol Biol 2009 Feb 13; 386 (1):163-77 ru.gif
Entry to sporulation in bacilli is governed by a histidine kinase phosphorelay, a variation of the predominant signal transduction mechanism in prokaryotes. Sda directly inhibits sporulation histidine kinases in response to DNA damage and replication defects. We determined a 2.0--resolution X-ray crystal structure of the intact cytoplasmic catalytic core [comprising the dimerization and histidine phosphotransfer domain (DHp domain), connected to the ATP binding catalytic domain] of the Geobacillus stearothermophilus sporulation kinase KinB complexed with Sda. Structural and biochemical analyses reveal that Sda binds to the base of the DHp domain and prevents molecular transactions with the DHp domain to which it is bound by acting as a simple molecular barricade. Sda acts to sterically block communication between the catalytic domain and the DHp domain, which is required for autophosphorylation, as well as to sterically block communication between the response regulator Spo0F and the DHp domain, which is required for phosphotransfer and phosphatase activities.

Cheung J., Hendrickson W.A. Structural analysis of ligand stimulation of the histidine kinase NarX. Structure 2009 Feb 13; 17 (2):190-201 ColumbiaUniversityintheCityofNewYorkcopy.gif
Histidine kinase receptors are a large family of membrane-spanning proteins found in many prokaryotes and some eukaryotes. They are a part of two-component signal transduction systems, which each comprise a sensor kinase and a response regulator and are involved with the regulation of many cellular processes. NarX is a histidine kinase receptor that responds to nitrate and nitrite to effect regulation of anaerobic respiration in various bacteria. We present high-resolution X-ray crystal structures of the periplasmic sensor domain from Escherichia coli NarX in a complex with nitrate and in the apo state. Our analysis reveals that nitrate-binding induces conformation changes that result in a piston-type displacement between the N- and C-terminal helices of the periplasmic domain. Such conformational changes might represent a conserved mechanism of signaling in histidine kinases by which ligand binding is communicated across the lipid bilayer.

Vorobiev S.M., Su M., Seetharaman J., Huang Y.J., Chen C.X., Maglaqui M., Janjua H., Proudfoot M., Yakunin A., Xiao R., Acton T.B., Montelione G.T., Tong L. Crystal structure of human retinoblastoma binding protein 9. Proteins 2009 Feb 1; 74 (2):526-9 ColumbiaUniversityintheCityofNewYorkcopy.gif
Rutgers U.
No abstract available.

  • January 2009
Price, W.N. II, Chen Y., Handelman S.K., Neely H., Manor P., Karlin R., Nair R., Liu J., Baran M., Everett J., Tong S.N., Forouhar F., Swaminathan S.S., Acton T., Xiao R., Luft J.R., Lauricella A., DeTitta G.T., Rost B., Montelione G.T., Hunt J.F. Understanding the physical properties that control protein crystallization by analysis of large-scale experimental data. Nat Biotechnol 2009 Jan; 27 (1):51-7 ColumbiaUniversityintheCityofNewYorkcopy.gif
Crystallization is the most serious bottleneck in highthroughput protein-structure determination by diffraction methods. We have used data mining of the large-scale experimental results of the Northeast Structural Genomics Consortium and experimental folding studies to characterize the biophysical properties that control protein crystallization. This analysis leads to the conclusion that crystallization propensity depends primarily on the prevalence of well-ordered surface epitopes capable of mediating interprotein interactions and is not strongly influenced by overall thermodynamic stability. We identify specific sequence features that correlate with crystallization propensity and that can be used to estimate the crystallization probability of a given construct. Analyses of entire predicted proteomes demonstrate substantial differences in the amino acidsequence properties of human versus eubacterial proteins, which likely reflect differences in biophysical properties, including crystallization propensity. Our thermodynamic measurements do not generally support previous claims regarding correlations between sequence properties and protein stability.

  • December 2008
Siemer A.B., McDermott A.E. Solid-State NMR on a Type III Antifreeze Protein in the Presence of Ice. J Am Chem Soc 2008 Dec 24; 130 (51):17394-9 ColumbiaUniversityintheCityofNewYorkcopy.gif
Antifreeze proteins (AFPs) are found in fish, insects, plants, and a variety of other organisms where they serve to prevent the growth of ice at subzero temperatures. Type III AFPs cloned from polar fishes have been studied extensively with X-ray crystallography, liquid-state NMR, and site directed mutagenesis and are, therefore, among the best characterized AFPs. A flat surface on the protein has previously been proposed to be the ice-binding site of type III AFP. The detailed nature of the ice binding remains controversial since it is not clear whether only polar or also hydrophobic residues are involved in ice binding and there is no structural information available of a type III AFP bound to ice. Here we present a high-resolution solid-state NMR study of a type III AFP (HPLC-12 isoform) in the presence of ice. The chemical-shift differences we detected between the frozen and the nonfrozen state agree well with the proposed ice-binding site. Furthermore, we found that the 1H T1 of HPLC-12 in frozen solution is very long compared to typical 1H of proteins in the solid state as for example of ubiquitin in frozen solution.

Chengmin Qian, Side Li, Jean Jakoncic, Lei Zeng, Martin J. Walsh, and Ming-Ming Zhou. Structure and Hemimethylated CpG Binding of the SRA Domain from Human UHRF1 J Bio Chem 2008 Dec 12; 283 (50):3449034494 mssm.gif
HumanUHRF1(ubiquitin-likePHDand RING finger 1) functions to maintain CpGDNAmethylation patterns through DNA replication by co-localizing with the DNA methyltransferase DNMT1 at chromatin in mammals. Recent studies show that UHRF1 binds selectively to hemimethylated CpG via its conserved SRA (SET- and RING finger-associated) domain. However, the underlying molecular mechanism is not known. Here, we report a 1.95 A˚ resolution crystal structure of the SRA domain of human UHRF1. Using NMR structure-guided mutagenesis, electrophoretic mobility shift assay, and fluorescence anisotropy analysis, we determined key amino acid residues for methyl-DNA binding that are conserved in the SRA domain.

Huaibin Chen, Chong-Feng Xu, Jinghong Ma, Anna V. Eliseenkova, Wanqing Li, Pamela M. Pollock, Nelly Pitteloud, W. Todd Miller, Thomas A. Neubert, and Moosa Mohammadi. A crystallographic snapshot of tyrosine trans-phosphorylation in action. PNAS 2008 Dec 16: 105 (50):1966019665 nyu.gif suny.gif
Tyrosine trans-phosphorylation is a key event in receptor tyrosine kinase signaling, yet, the structural basis for this process has eluded definition. Here, we present the crystal structure of the FGF receptor 2 kinases caught in the act of trans-phosphorylation of Y769, the major C-terminal phosphorylation site. The structure reveals that enzyme- and substrate-acting kinases engage each other through elaborate and specific interactions not only in the immediate vicinity of Y769 and the enzyme active site, but also in regions that are as much of 18 away from D626, the catalytic base in the enzyme active site. These interactions lead to an unprecedented level of specificity and precision during the trans- phosphorylation on Y769. Time-resolved mass spectrometry analysis supports the observed mechanism of trans-phosphorylation. Our data provide a molecular framework for understanding the mechanism of action of Kallmann syndrome mutations and the order of trans-phosphorylation reactions in FGFRs. We propose that the salient mechanistic features of Y769 transphosphorylation are applicable to trans-phosphorylation of the equivalent major phosphorylation sites in many other RTKs.

Milstein O., Tseng S.Y., Starr T., Llodra J., Nans A., Liu M., Wild M.K., van der Merwe P.A., Stokes D.L., Reisner Y., Dustin M.L. Nanoscale increases in CD2-CD48-mediated intermembrane spacing decrease adhesion and reorganize the immunological synapse. J Biol Chem 2008 Dec 5; 283 (49):34414-22 nyu.gif
The relationship between intermembrane spacing, adhesion efficiency, and lateral organization of adhesion receptors has not been established for any adhesion system. We have utilized the CD2 ligand CD48 with two (wild type CD48 (CD48-WT)), four (CD48-CD2), or five (CD48-CD22) Ig-like domains. CD48-WT was 10-fold more efficient in mediating adhesion than CD48-CD2 or CD48-CD22. Electron tomography of contact areas with planar bilayers demonstrated average intermembrane spacing of 12.8 nm with CD48-WT, 14.7 nm with CD48-CD2, and 15.6 nm with CD48-CD22. Both CD48-CD2 and CD48-CD22 chimeras segregated completely from CD48-WT in mixed contact areas. In contrast, CD48-CD2 and CD48-CD22 co-localized when mixed contacts were formed. Confocal imaging of immunological synapses formed between primary T lymphocytes and Chinese hamster ovary cells presenting major histocompatibility complex-peptide complexes, and different forms of CD48 demonstrated that CD48-CD2 and CD48-CD22 induce an eccentric CD2/T cell antigen receptor cluster. We propose that this reorganization of the immunological synapse sequesters the T cell antigen receptor in a location where it cannot interact with its ligand and dramatically reduces T cell sensitivity.

  • November 2008
Parish, D., Benach, J., Liu, G., Singarapu, R., Xiao, R., Acton, T., Hunt, J., Montelione, G., Szyperski, T. Protein Chaperones Q8ZP25_SALTY from Salmonella Typhimurium and HYAE_ECOLI from Escherichia coli Exhibit Thioredoxin-like Structures Despite Lack of Canonical Thioredoxin Active Site Sequence Motif. J Struct Funt Genomics 2008 Nov 26 9 :41-49 ColumbiaUniversityintheCityofNewYorkcopy.gif suny.gif
The structure of the 142-residue protein Q8ZP 25_SALTY encoded in the genome of Salmonella typhimurium LT2 was determined independently by NMR and X-ray crystallography, and the structure of the 140-residue protein HYAE_ECOLI encoded in the genome of Escherichia coli was determined byNMR. The two proteins belong to Pfam (Finn et al. 34:D247D251, 2006) PF07449, which currently comprises 50 members, and belongs itself to the thioredoxin-like clan. However, protein HYAE_ ECOLI and the other proteins of Pfam PF07449 do not contain the canonical Cys-X-X-Cys active site sequence motif of thioredoxin. Protein HYAE_ECOLI was previously classified as a [NiFe] drogenase-1 specific chaperone interacting with the twin-arginine translocation (Tat) signal peptide. The structures presented here exhibit the expected thioredoxin-like fold and support the view that members of Pfam family PF07449 specifically interact with Tat signal peptides.

Tan D., Rice W.J., Sosa H. Structure of the Kinesin13 Ring Complex. Structure 2008 Nov 12; 16 :17321739 aeco.gif
Toinvestigate the mechanismof kinesin13-inducedmicrotubule depolymerization, we have calculated a three-dimensional (3D)mapof the kinesin13-microtubule ring complex, using cryo-electron microscopy (cryo-EM) and image analysis. An atomic model of the complex was produced by docking the crystal structures of tubulin and a kinesin13 motor domain (MD) into the 3D map. The model reveals a snapshot of the depolymerization mechanism by providing a 3D view of the complex formed between the kinesin13 MD and a curved tubulin protofilament (pf). It suggests that contactsmediated by kinesin13 class-specific residues in the putative microtubule-binding site stabilize intra-dimer tubulin curvature. In addition, a tubulinbinding site on the kinesin13 MD was identified. Mutations at this class-conserved site selectively disrupt the formation of microtubule-associated ring complexes.

Kalyanaraman C., Imker H.J., Fedorov A.A., Fedorov E.V., Glasner M.E., Babbitt P.C., Almo S.C., Gerlt J.A., Jacobson M.P. Discovery of a dipeptide epimerase enzymatic function guided by homology modeling and virtual screening. Structure 2008 Nov 12; 16 (11):1668-77 aeco.gif
U. Md
We have developed a computational approach to aid the assignment of enzymatic function for uncharacterized proteins that uses homology modeling to predict the structure of the binding site and in silico docking to identify potential substrates. We apply this method to proteins in the functionally diverse enolase superfamily that are homologous to the characterized L-Ala-D/L-Glu epimerase from Bacillus subtilis. In particular, a protein from Thermotoga martima was predicted to have different substrate specificity, which suggests that it has a different, but as yet unknown, biological function. This prediction was experimentally confirmed, resulting in the assignment of epimerase activity for L-Ala-D/L-Phe, L-Ala-D/L-Tyr, and L-Ala-D/L-His, whereas the enzyme is annotated incorrectly in GenBank as muconate cycloisomerase. Subsequently, crystal structures of the enzyme were determined in complex with three substrates, showing close agreement with the computational models and revealing the structural basis for the observed substrate selectivity.

Banik, J.J., and Brady, S.F. Cloning and characterization of new glycopeptide gene clusters found in an environmental DNA megalibrary. Proc Natl Acad Sci U S A 2008 Nov 11; 105 (45):17273-7 ru.gif
Glycopeptide antibiotics have long served as drugs of last resort for the treatment of antibiotic-resistant gram-positive bacterial infections. Resistance to the clinically relevant glycopeptides, vancomycin and teicoplanin, threatens to undermine the usefulness of this important class of antibiotics. DNA extracted from a geographically diverse collection of soil samples was screened by PCR for the presence of sequences related to OxyC, an oxidative coupling enzyme found in glycopeptide biosynthetic gene clusters. Every soil sample examined contained at least 1 unique OxyC gene sequence. In an attempt to access the biosynthetic gene clusters associated with these OxyC sequences, a 10,000,000-membered environmental DNA (eDNA) megalibrary was created from a single soil sample. Two unique glycopeptide gene clusters were recovered from this eDNA megalibrary. Using the teicoplanin aglycone and the 3 sulfotransferases found in one of these gene clusters, mono-, di-, and trisulfated glycopeptide congeners were produced. The high frequency with which OxyC genes were found in environmental samples indicates that soil eDNA libraries are likely to be a rewarding source of glycopeptide gene clusters. Enzymes found in these gene clusters should be useful for generating new glycopeptides analogs. Environmental DNA megalibraries, like the one constructed for this study, can provide access to many of the natural product biosynthetic gene clusters that are predicted to be present in soil microbiomes.

Pan Y., Weng J., Kabaleeswaran V., Li H., Cao Y., Bhosle R.C., Zhou M. Cortisone dissociates the Shaker family K+ channels from their beta subunits. Nat Chem Biol 2008 Nov; 4 (11):708-14 ColumbiaUniversityintheCityofNewYorkcopy.gif
The Shaker family voltage-dependent potassium channels (Kv1) are expressed in a wide variety of cells and are essential for cellular excitability. In humans, loss-of-function mutations of Kv1 channels lead to hyperexcitability and are directly linked to episodic ataxia and atrial fibrillation. All Kv1 channels assemble with beta subunits (Kv betas), and certain Kv betas, for example Kv beta 1, have an N-terminal segment that closes the channel by the N-type inactivation mechanism. In principle, dissociation of Kv beta 1, although never reported, should eliminate inactivation and thus potentiate Kv1 current. We found that cortisone increases rat Kv1 channel activity by binding to Kv beta 1. A crystal structure of the Kv beta-cortisone complex was solved to 1.82-A resolution and revealed novel cortisone binding sites. Further studies demonstrated that cortisone promotes dissociation of Kv beta. The new mode of channel modulation may be explored by native or synthetic ligands to fine-tune cellular excitability.

  • September 2008
Vila J.A., Aramini J.M., Rossi P., Kuzin A., Su M., Seetharaman J., Xiao R., Tong L., Montelione G.T., Scheraga H.A. Quantum chemical 13C(alpha) chemical shift calculations for protein NMR structure determination, refinement, and validation. Proc Natl Acad Sci U S A 2008 Sep 23; 105 (38):14389-94 Cornell U.,
CNICT, Argentina
Rutgers U., ColumbiaUniversityintheCityofNewYorkcopy.gif , UMDNJ
A recently determined set of 20 NMR-derived conformations of a 48-residue all-alpha-helical protein, (PDB ID code 2JVD), is validated here by comparing the observed (13)C(alpha) chemical shifts with those computed at the density functional level of theory. In addition, a recently introduced physics-based method, aimed at determining protein structures by using NOE-derived distance constraints together with observed and computed (13)C(alpha) chemical shifts, was applied to determine a new set of 10 conformations, (Set-bt), as a blind test for the same protein. A cross-validation of these two sets of conformations in terms of the agreement between computed and observed (13)C(alpha) chemical shifts, several stereochemical quality factors, and some NMR quality assessment scores reveals the good quality of both sets of structures. We also carried out an analysis of the agreement between the observed and computed (13)C(alpha) chemical shifts for a slightly longer construct of the protein solved by x-ray crystallography at 2.0-A resolution (PDB ID code 3BHP) with an identical amino acid residue sequence to the 2JVD structure for the first 46 residues. Our results reveal that both of the NMR-derived sets, namely 2JVD and Set-bt, are somewhat better representations of the observed (13)C(alpha) chemical shifts in solution than the 3BHP crystal structure. In addition, the (13)C(alpha)-based validation analysis appears to be more sensitive to subtle structural differences across the three sets of structures than any other NMR quality-assessment scores used here, and, although it is computationally intensive, this analysis has potential value as a standard procedure to determine, refine, and validate protein structures.

Deng Y., Liu J., Zheng Q., Li Q., Kallenbach N.R., Lu M. A heterospecific leucine zipper tetramer. Chem Biol 2008 Sep 22; 15 (9):908-19 nyu.gif weil.gif
Protein-protein interactions play an essential role in the assembly of the macromolecular complexes that form functional networks and control cellular behavior. Elucidating principles of molecular recognition governing potentially complex interfaces is a challenging goal for structural and systems biology. Extensive studies of alpha-helical coiled coils have provided fundamental insight into the determinants of one seemingly tractable class of oligomeric protein interfaces. We report here that two different valine-containing mutants of the GCN4 leucine zipper that fold individually as four-stranded coiled coils associate preferentially in mixtures to form an antiparallel, heterotetrameric structure. X-ray crystallographic analysis reveals that the coinciding hydrophobic interfaces of the hetero- and homotetramers differ in detail, thereby controlling their partnering and structural specificity. Equilibrium disulfide exchange and thermal denaturation experiments show that the 50-fold preference for heterospecificity is determined by interfacial van der Waals interactions and hydrophobicity. Parallel studies of two alanine-containing variants confirm the above-mentioned interpretation of the basis and mechanism of this heterospecificity. Our results suggest that coiled-coil recognition is an inherently geometric process in which heterotypic interaction specificity derives from a complementarity of both shape and chemistry.

Chan K.K., Fedorov A.A., Fedorov E.V., Almo S.C., Gerlt J.A. Structural basis for substrate specificity in phosphate binding (beta/alpha)8-barrels: D-allulose 6-phosphate 3-epimerase from Escherichia coli K-12. Biochemistry 2008 Sep 9; 47 (36):9608-17 aeco.gif
Enzymes that share the (beta/alpha) 8-barrel fold catalyze a diverse range of reactions. Many utilize phosphorylated substrates and share a conserved C-terminal (beta/alpha) 2-quarter barrel subdomain that provides a binding motif for the dianionic phosphate group. We recently reported functional and structural studies of d-ribulose 5-phosphate 3-epimerase (RPE) from Streptococcus pyogenes that catalyzes the equilibration of the pentulose 5-phosphates d-ribulose 5-phosphate and d-xylulose 5-phosphate in the pentose phosphate pathway [J. Akana, A. A. Fedorov, E. Fedorov, W. R. P. Novack, P. C. Babbitt, S. C. Almo, and J. A. Gerlt (2006) Biochemistry 45, 2493-2503]. We now report functional and structural studies of d-allulose 6-phosphate 3-epimerase (ALSE) from Escherichia coli K-12 that catalyzes the equilibration of the hexulose 6-phosphates d-allulose 6-phosphate and d-fructose 6-phosphate in a catabolic pathway for d-allose. ALSE and RPE prefer their physiological substrates but are promiscuous for each other's substrate. The active sites (RPE complexed with d-xylitol 5-phosphate and ALSE complexed with d-glucitol 6-phosphate) are superimposable (as expected from their 39% sequence identity), with the exception of the phosphate binding motif. The loop following the eighth beta-strand in ALSE is one residue longer than the homologous loop in RPE, so the binding site for the hexulose 6-phosphate substrate/product in ALSE is elongated relative to that for the pentulose 5-phosphate substrate/product in RPE. We constructed three single-residue deletion mutants of the loop in ALSE, DeltaT196, DeltaS197 and DeltaG198, to investigate the structural bases for the differing substrate specificities; for each, the promiscuity is altered so that d-ribulose 5-phosphate is the preferred substrate. The changes in k cat/ K m are dominated by changes in k cat, suggesting that substrate discrimination results from differential transition state stabilization. In both ALSE and RPE, the phosphate group hydrogen bonds not only with the conserved motif but also with an active site loop following the sixth beta-strand, providing a potential structural mechanism for coupling substrate binding with catalysis.

  • March 2008
Xiang, S., and Tong, L. Crystal Structures of Human and Staphylococcus aureus Pyruvate Carbozylase and Molecular Insights into the Carboxyltransfer Reaction. Nat Struct Mol Biol, 15 (3): 295-302 ColumbiaUniversityintheCityofNewYorkcopy.gif
Pyruvate carboxylase (PC) catalyzes the biotin-dependent production of oxaloacetate and has important roles in gluconeogenesis, lipogenesis, insulin secretion and other cellular processes. PC contains the biotin carboxylase (BC), carboxyltransferase (CT) and biotin-carboxyl carrier protein (BCCP) domains. We report here the crystal structures at 2.8-A resolution of full-length PC from Staphylococcus aureus and the C-terminal region (missing only the BC domain) of human PC. A conserved tetrameric association is observed for both enzymes, and our structural and mutagenesis studies reveal a previously uncharacterized domain, the PC tetramerization (PT) domain, which is important for oligomerization. A BCCP domain is located in the active site of the CT domain, providing the first molecular insights into how biotin participates in the carboxyltransfer reaction. There are dramatic differences in domain positions in the monomer and the organization of the tetramer between these enzymes and the PC from Rhizobium etli.

Ling, W., Regatte, R.R., Schweitzer, M.E., and Jerschow, A. Characterization of bovine patellar cartilage by NMR. NMR Biomed 2008 Mar; 21 (3):289-95 nyu.gif
Metabolic and structural changes in cartilage tissue are thought to be at the root of degenerative joint disease. We identify here the NMR resonances in bovine patellar cartilage tissue by static and high-resolution magic angle spinning (HRMAS) NMR spectroscopy, (1)H-(13)C heteronuclear single-quantum correlation (HSQC) spectroscopy, total correlation spectroscopy (TOCSY), and saturation transfer experiments. Some differences between the patellar cartilage samples studied here and earlier nasal cartilage and intervertebrate disc studies were found. In addition, we show assignments downfield of the water signal, which also includes the assignment of amide and hydroxy protons on the basis of their exchangeability with water. These results will allow an identification of spectroscopic markers of cartilage degradation using techniques such as chemical exchange saturation transfer imaging.

  • February 2008
Lin S.C., Chung J.Y., Lamothe B., Rajashankar K., Lu M., Lo Y.C., Lam A.Y., Darnay B.G., Wu H. Molecular basis for the unique deubiquitinating activity of the NF-kappaB inhibitor A20. J Mol Biol 2008 Feb 15; 376 (2):526-40 weil.gif
Nuclear factor kappaB (NF-kappaB) activation in tumor necrosis factor, interleukin-1, and Toll-like receptor pathways requires Lys63-linked nondegradative polyubiquitination. A20 is a specific feedback inhibitor of NF-kappaB activation in these pathways that possesses dual ubiquitin-editing functions. While the N-terminal domain of A20 is a deubiquitinating enzyme (DUB) for Lys63-linked polyubiquitinated signaling mediators such as TRAF6 and RIP, its C-terminal domain is a ubiquitin ligase (E3) for Lys48-linked degradative polyubiquitination of the same substrates. To elucidate the molecular basis for the DUB activity of A20, we determined its crystal structure and performed a series of biochemical and cell biological studies. The structure reveals the potential catalytic mechanism of A20, which may be significantly different from papain-like cysteine proteases. Ubiquitin can be docked onto a conserved A20 surface; this interaction exhibits charge complementarity and no steric clash. Surprisingly, A20 does not have specificity for Lys63-linked polyubiquitin chains. Instead, it effectively removes Lys63-linked polyubiquitin chains from TRAF6 without dissembling the chains themselves. Our studies suggest that A20 does not act as a general DUB but has the specificity for particular polyubiquitinated substrates to assure its fidelity in regulating NF-kappaB activation in the tumor necrosis factor, interleukin-1, and Toll-like receptor pathways.

List of publications by institution, possibly not yet including all above

Highlights of NYSBC associated publications through 2004

This topic: Main > ScientificReport > RecentPreprintsAndReprints > PapersAssociated
History: r14 - 06 Sep 2008 - 10:00:37 - DavidCowburn
 
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