RESUMEN
To enhance our understanding of the potential therapeutic utility of insulin-degrading enzyme (IDE) in Alzheimer's disease (AD), we studied in vitro IDE-mediated degradation of different amyloid-beta (Aß) peptide aggregation states. Our findings show that IDE activity is driven by the dynamic equilibrium between Aß monomers and higher ordered aggregates. We identify Met(35)-Val(36) as a novel IDE cleavage site in the Aß sequence and show that Aß fragments resulting from IDE cleavage form non-toxic amorphous aggregates. These findings need to be taken into account in therapeutic strategies designed to increase Aß clearance in AD patients by modulating IDE activity.
Asunto(s)
Péptidos beta-Amiloides/química , Insulisina/fisiología , Agregado de Proteínas , Secuencia de Aminoácidos , Datos de Secuencia MolecularRESUMEN
Sugar binding by a cell surface â¼29 kDa lectin (RSL) from the bacterium Ralstonia solanacearum was characterized by NMR spectroscopy. The complexes formed with four monosaccharides and four fucosides were studied. Complete resonance assignments and backbone dynamics were determined for RSL in the sugar-free form and when bound to l-fucose or d-mannose. RSL was found to interact with both the α- and the ß-anomer of l-fucose and the "fucose like" sugars d-arabinose and l-galactose. Peak splitting was observed for some resonances of the binding site residues. The assignment of the split signals to the α- or ß-anomer was confirmed by comparison with the spectra of RSL bound to methyl-α-l-fucoside or methyl-ß-l-fucoside. The backbone dynamics of RSL were sensitive to the presence of ligand, with the protein adopting a more compact structure upon binding to l-fucose. Taking advantage of tryptophan residues in the binding sites, we show that the indole resonance is an excellent reporter on ligand binding. Each sugar resulted in a distinct signature of chemical shift perturbations, suggesting that tryptophan signals are a sufficient probe of sugar binding.
Asunto(s)
Proteínas Bacterianas/metabolismo , Fucosa/metabolismo , Lectinas/metabolismo , Ralstonia solanacearum/metabolismo , Secuencia de Aminoácidos , Proteínas Bacterianas/química , Fucosa/análogos & derivados , Lectinas/química , Manosa/metabolismo , Modelos Moleculares , Datos de Secuencia Molecular , Unión Proteica , Ralstonia solanacearum/química , Alineación de SecuenciaRESUMEN
Design of a new catalytic function in proteins, apart from its inherent practical value, is important for fundamental understanding of enzymatic activity. Using a computationally inexpensive, minimalistic approach that focuses on introducing a single highly reactive residue into proteins to achieve catalysis we converted a 74-residue-long C-terminal domain of calmodulin into an efficient esterase. The catalytic efficiency of the resulting stereoselective, allosterically regulated catalyst, nicknamed AlleyCatE, is higher than that of any previously reported de novo designed esterases. The simplicity of our design protocol should complement and expand the capabilities of current state-of-art approaches to protein design. These results show that even a small nonenzymatic protein can efficiently attain catalytic activities in various reactions (Kemp elimination, ester hydrolysis, retroaldol reaction) as a result of a single mutation. In other words, proteins can be just one mutation away from becoming entry points for subsequent evolution.
Asunto(s)
Enzimas/química , Mutación , Proteínas/química , Catálisis , Dicroismo Circular , Cinética , Resonancia Magnética Nuclear Biomolecular , Proteínas/genética , Proteolisis , Espectrofotometría UltravioletaRESUMEN
Toxin-antitoxin (TA) modules are pairs of genes essential for bacterial regulation upon environmental stresses. The mazEF module encodes the MazF toxin and its cognate MazE antitoxin. The highly dynamic MazE possesses an N-terminal DNA binding domain through which it can negatively regulate its own promoter. Despite being one of the first TA systems studied, transcriptional regulation of Escherichia coli mazEF remains poorly understood. This paper presents the solution structure of C-terminal truncated E. coli MazE and a MazE-DNA model with a DNA palindrome sequence â¼ 10 bp upstream of the mazEF promoter. The work has led to a transcription regulator-DNA model, which has remained elusive thus far in the E. coli toxin-antitoxin family. Multiple complementary techniques including NMR, SAXS and ITC show that the long intrinsically disordered C-termini in MazE, required for MazF neutralization, does not affect the interactions between the antitoxin and its operator. Rather, the MazE C-terminus plays an important role in the MazF binding, which was found to increase the MazE affinity for the palindromic single site operator.
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ADN Bacteriano/química , Proteínas de Unión al ADN/química , Proteínas de Escherichia coli/química , Factores de Transcripción/química , ADN Bacteriano/metabolismo , Proteínas de Unión al ADN/metabolismo , Endorribonucleasas/metabolismo , Proteínas de Escherichia coli/metabolismo , Secuencias Invertidas Repetidas , Modelos Moleculares , Regiones Operadoras Genéticas , Unión Proteica , Estructura Terciaria de Proteína , Factores de Transcripción/metabolismoRESUMEN
The Staphylococcus aureus genome contains three toxin-antitoxin modules, including one mazEF module, SamazEF. Using an on-column separation protocol we are able to obtain large amounts of wild-type SaMazF toxin. The protein is well-folded and highly resistant against thermal unfolding but aggregates at elevated temperatures. Crystallographic and nuclear magnetic resonance (NMR) solution studies show a well-defined dimer. Differences in structure and dynamics between the X-ray and NMR structural ensembles are found in three loop regions, two of which undergo motions that are of functional relevance. The same segments also show functionally relevant dynamics in the distantly related CcdB family despite divergence of function. NMR chemical shift mapping and analysis of residue conservation in the MazF family suggests a conserved mode for the inhibition of MazF by MazE.
Asunto(s)
Proteínas Bacterianas/química , Toxinas Bacterianas/química , Staphylococcus aureus , Proteínas Bacterianas/aislamiento & purificación , Proteínas Bacterianas/metabolismo , Toxinas Bacterianas/aislamiento & purificación , Toxinas Bacterianas/metabolismo , Sitios de Unión , Proteínas de Unión al ADN/química , Endorribonucleasas/química , Proteínas de Escherichia coli/química , Modelos Moleculares , Conformación Proteica , Desplegamiento ProteicoRESUMEN
Antitoxins from prokaryotic type II toxin-antitoxin modules are characterized by a high degree of intrinsic disorder. The description of such highly flexible proteins is challenging because they cannot be represented by a single structure. Here, we present a combination of SAXS and NMR data to describe the conformational ensemble of the PaaA2 antitoxin from the human pathogen E. coli O157. The method encompasses the use of SAXS data to filter ensembles out of a pool of conformers generated by a custom NMR structure calculation protocol and the subsequent refinement by a block jackknife procedure. The final ensemble obtained through the method is validated by an established residual dipolar coupling analysis. We show that the conformational ensemble of PaaA2 is highly compact and that the protein exists in solution as two preformed helices, connected by a flexible linker, that probably act as molecular recognition elements for toxin inhibition.
Asunto(s)
Antitoxinas/química , Toxinas Bacterianas/química , Escherichia coli O157/química , Proteínas de Escherichia coli/química , Secuencia de Aminoácidos , Antitoxinas/genética , Toxinas Bacterianas/genética , Escherichia coli O157/genética , Proteínas de Escherichia coli/genética , Humanos , Espectroscopía de Resonancia Magnética , Modelos Moleculares , Datos de Secuencia Molecular , Conformación Proteica , Dispersión del Ángulo Pequeño , Difracción de Rayos XRESUMEN
Uropathogenic Escherichia coli cause urinary tract infections by adhering to mannosylated receptors on the human urothelium via the carbohydrate-binding domain of the FimH adhesin (FimHL). Numerous α-d-mannopyranosides, including α-d-heptyl mannose (HM), inhibit this process by interacting with FimHL. To establish the molecular basis of the high-affinity HM binding, we solved the solution structure of the apo form and the crystal structure of the FimHL-HM complex. NMR relaxation analysis revealed that protein dynamics were not affected by the sugar binding, yet HM addition promoted protein dimerization, which was further confirmed by small-angle X-ray scattering. Finally, to address the role of Y48, part of the "tyrosine gate" believed to govern the affinity and specificity of mannoside binding, we characterized the FimHL Y48A mutant, whose conformational, dynamical, and HM binding properties were found to be very similar to those of the wild-type protein.
Asunto(s)
Adhesinas de Escherichia coli/química , Proteínas Fimbrias/química , Manosa/análogos & derivados , Adhesinas de Escherichia coli/metabolismo , Dimerización , Proteínas Fimbrias/metabolismo , Manosa/química , Manosa/metabolismo , Modelos Moleculares , Resonancia Magnética Nuclear Biomolecular , Unión Proteica , Conformación ProteicaRESUMEN
Src homology 2 (SH2) domains have an important role in the regulation of protein activity and intracellular signaling processes. They are geared to bind to specific phosphotyrosine (pY) motifs, with a substrate sequence specificity depending on the three amino acids immediately C-terminal to the pY. Here we report for the first time the (1)H, (15)N and (13)C backbone and side-chain chemical shift assignments for the C-terminal SH2 domain of the human protein tyrosine phosphatase PTPN11, both in its free and bound forms, where the ligand in the latter corresponds to a specific sequence of the human erythropoietin receptor.
Asunto(s)
Resonancia Magnética Nuclear Biomolecular , Proteína Tirosina Fosfatasa no Receptora Tipo 11/química , Proteína Tirosina Fosfatasa no Receptora Tipo 11/metabolismo , Dominios Homologos src , Secuencia de Aminoácidos , Humanos , Modelos Moleculares , Datos de Secuencia Molecular , Fragmentos de Péptidos/metabolismo , Unión ProteicaRESUMEN
TAX1BP1 is a novel ubiquitin-binding adaptor protein involved in the negative regulation of the NF-kappaB transcription factor, which is a key player in inflammatory responses, immunity and tumorigenesis. TAX1BP1 recruits A20 to the ubiquitinated signaling proteins TRAF6 and RIP1, leading to their A20-mediated deubiquitination and the disruption of IL-1-induced and TNF-induced NF-kappaB signaling, respectively. The two zinc fingers localized at its C-terminus function as novel ubiquitin-binding domains (UBZ, ubiquitin-binding zinc finger). Here we present for the first time both the solution and crystal structures of two classical UBZ domains in tandem within the human TAX1BP1. The relative orientation of the two domains is slightly different in the X-ray structure with respect to the NMR structure, indicating some degree of conformational flexibility, which is rationalized by NMR relaxation data. The observed degree of flexibility and stability between the two UBZ domains might have consequences on the recognition mechanism of interacting partners.
Asunto(s)
Péptidos y Proteínas de Señalización Intracelular/química , Péptidos y Proteínas de Señalización Intracelular/metabolismo , Proteínas de Neoplasias/química , Proteínas de Neoplasias/metabolismo , Ubiquitina/metabolismo , Secuencias de Aminoácidos , Secuencia de Aminoácidos , Cristalografía por Rayos X , Humanos , Espectroscopía de Resonancia Magnética , Datos de Secuencia Molecular , Unión Proteica , Estructura Terciaria de Proteína , Dispersión del Ángulo Pequeño , Homología de Secuencia de Aminoácido , Transducción de SeñalRESUMEN
Toxin-antitoxin (TA) modules in bacteria are involved in pathogenesis, antibiotic stress response, persister formation and programmed cell death. The toxin Doc, from the phd/doc module, blocks protein synthesis by targeting the translation machinery. Despite a large wealth of biophysical and biochemical data on the regulatory aspects of the operon transcription and role of Doc co-activator and co-repressor, little is still know on the molecular basis of Doc toxicity. Structural information about this toxin is only available for its inhibited state bound to the antitoxin Phd. Here we report the (1)H, (15)N and (13)C backbone and side chain chemical shift assignments of the toxin Doc from of bacteriophage P1 (the model protein from this family of TA modules) in its free state. The BMRB accession number is 18899.
Asunto(s)
Bacteriófago P1/metabolismo , Resonancia Magnética Nuclear Biomolecular , Proteínas Virales/química , Secuencia de Aminoácidos , Isótopos de Carbono , Hidrógeno , Datos de Secuencia Molecular , Isótopos de Nitrógeno , Estructura Secundaria de ProteínaRESUMEN
Fic proteins are ubiquitous in all of the domains of life and have critical roles in multiple cellular processes through AMPylation of (transfer of AMP to) target proteins. Doc from the doc-phd toxin-antitoxin module is a member of the Fic family and inhibits bacterial translation by an unknown mechanism. Here we show that, in contrast to having AMPylating activity, Doc is a new type of kinase that inhibits bacterial translation by phosphorylating the conserved threonine (Thr382) of the translation elongation factor EF-Tu, rendering EF-Tu unable to bind aminoacylated tRNAs. We provide evidence that EF-Tu phosphorylation diverged from AMPylation by antiparallel binding of the NTP relative to the catalytic residues of the conserved Fic catalytic core of Doc. The results bring insights into the mechanism and role of phosphorylation of EF-Tu in bacterial physiology as well as represent an example of the catalytic plasticity of enzymes and a mechanism for the evolution of new enzymatic activities.
Asunto(s)
Proteínas de Escherichia coli/metabolismo , Nucleotidiltransferasas/metabolismo , Proteínas de Escherichia coli/genética , Regulación Bacteriana de la Expresión Génica , Guanosina Trifosfato/genética , Guanosina Trifosfato/metabolismo , Modelos Moleculares , Mutación , Nucleotidiltransferasas/genética , Factor Tu de Elongación Peptídica/genética , Factor Tu de Elongación Peptídica/metabolismo , Fosforilación , Pliegue de Proteína , ARN de Transferencia/genética , ARN de Transferencia/metabolismoRESUMEN
SH3 domains constitute a new type of ubiquitin-binding domains. We previously showed that the third SH3 domain (SH3-C) of CD2AP binds ubiquitin in an alternative orientation. We have determined the structure of the complex between first CD2AP SH3 domain and ubiquitin and performed a structural and mutational analysis to decipher the determinants of the SH3-C binding mode to ubiquitin. We found that the Phe-to-Tyr mutation in CD2AP and in the homologous CIN85 SH3-C domain does not abrogate ubiquitin binding, in contrast to previous hypothesis and our findings for the first two CD2AP SH3 domains. The similar alternative binding mode of the SH3-C domains of these related adaptor proteins is characterised by a higher affinity to C-terminal extended ubiquitin molecules. We conclude that CD2AP/CIN85 SH3-C domain interaction with ubiquitin constitutes a new ubiquitin-binding mode involved in a different cellular function and thus changes the previously established mechanism of EGF-dependent CD2AP/CIN85 mono-ubiquitination.
Asunto(s)
Ubiquitina/química , Dominios Homologos src , Proteínas Adaptadoras Transductoras de Señales/química , Proteínas Adaptadoras Transductoras de Señales/genética , Proteínas Adaptadoras Transductoras de Señales/metabolismo , Proteínas del Citoesqueleto/química , Proteínas del Citoesqueleto/genética , Proteínas del Citoesqueleto/metabolismo , Modelos Moleculares , Mutación , Resonancia Magnética Nuclear Biomolecular , Unión Proteica , Conformación Proteica , Dominios y Motivos de Interacción de Proteínas , Ubiquitina/metabolismoRESUMEN
Here we describe paramagnetic NMR analysis of the low- and high-spin forms of yeast cytochrome c peroxidase (CcP), a 34 kDa heme enzyme involved in hydroperoxide reduction in mitochondria. Starting from the assigned NMR spectra of a low-spin CN-bound CcP and using a strategy based on paramagnetic pseudocontact shifts, we have obtained backbone resonance assignments for the diamagnetic, iron-free protein and the high-spin, resting-state enzyme. The derived chemical shifts were further used to determine low- and high-spin magnetic susceptibility tensors and the zero-field splitting constant (D) for the high-spin CcP. The D value indicates that the latter contains a hexacoordinate heme species with a weak field ligand, such as water, in the axial position. Being one of the very few high-spin heme proteins analyzed in this fashion, the resting state CcP expands our knowledge of the heme coordination chemistry in biological systems.
Asunto(s)
Citocromo-c Peroxidasa/química , Espectroscopía de Resonancia por Spin del Electrón/métodos , Hemoproteínas/química , Resonancia Magnética Nuclear Biomolecular/métodos , Levaduras/enzimología , Citocromo-c Peroxidasa/análisis , Mitocondrias/enzimologíaRESUMEN
Here we present a solution NMR study of the complex between yeast cytochrome c (Cc) and cytochrome c peroxidase (CcP), a paradigm for understanding the biological electron transfer. Performed for the first time, the CcP-observed heteronuclear NMR experiments were used to probe the Cc binding in solution. Combining the Cc- and CcP-detected experiments, the binding interface on both proteins was mapped out, confirming that the X-ray structure of the complex is maintained in solution. Using NMR titrations and chemical shift perturbation analysis, we show that the interaction is independent of the CcP spin-state and is only weakly affected by the Cc redox state. Based on these findings, we argue that the complex of the ferrous Cc and the cyanide-bound CcP is a good mimic of the catalytically-active Cc-CcP compound I species. Finally, no chemical shift perturbations due to the Cc binding at the low-affinity CcP site were observed at low ionic strength. We discuss possible reasons for the absence of the effects and outline future research directions.
Asunto(s)
Citocromo-c Peroxidasa/química , Citocromos c/química , Resonancia Magnética Nuclear Biomolecular , Algoritmos , Citocromo-c Peroxidasa/metabolismo , Citocromos c/metabolismo , Cinética , Modelos Moleculares , Conformación Molecular , Unión ProteicaRESUMEN
The CD2AP (CD2-associated protein) and CIN85 (Cbl-interacting protein of 85 kDa) adaptor proteins each employ three Src homology 3 (SH3) domains to cluster protein partners and ensure efficient signal transduction and down-regulation of tyrosine kinase receptors. Using NMR, isothermal titration calorimetry and small-angle X-ray scattering methods, we have characterized several binding modes of the N-terminal SH3 domain (SH3A) of CD2AP and CIN85 with two natural atypical proline-rich regions in CD2 (cluster of differentiation 2) and Cbl-b (Casitas B-lineage lymphoma), and compared these data with previous studies and published crystal structures. Our experiments show that the CD2AP-SH3A domain forms a type II dimer with CD2 and both type I and type II dimeric complexes with Cbl-b. Like CD2AP, the CIN85-SH3A domain forms a type II complex with CD2, but a trimeric complex with Cbl-b, whereby the type I and II interactions take place at the same time. Together, these results explain how multiple interactions among similar SH3 domains and ligands produce a high degree of diversity in tyrosine kinase, cell adhesion or T-cell signaling pathways.
Asunto(s)
Proteínas Adaptadoras Transductoras de Señales/química , Antígenos CD2/química , Proteínas del Citoesqueleto/química , Proteínas Proto-Oncogénicas c-cbl/química , Secuencia de Aminoácidos , Humanos , Enlace de Hidrógeno , Modelos Moleculares , Datos de Secuencia Molecular , Resonancia Magnética Nuclear Biomolecular , Prolina , Unión Proteica , Estructura Secundaria de Proteína , Dispersión del Ángulo Pequeño , Termodinámica , Volumetría , Difracción de Rayos X , Dominios Homologos srcRESUMEN
The VAR2CSA protein has been closely associated with pregnancy-associated malaria and is recognized as the main adhesin exposed on the surface of Plasmodium falciparum-infected erythrocytes. Chondroitin sulfate A was identified as the main host receptor in the placenta. Single-domain heavy-chain camelid antibodies, more commonly called nanobodies, were selected and produced against the DBL6â-FCR3 domain of VAR2CSA. Crystals of two specific nanobodies, Nb2907 and Nb2919, identified as strong binders to DBL6â-FCR3 and the full-length VAR2CSA exposed on the surface of FCR3 P. falciparum-infected erythrocytes, were obtained. Crystals of Nb2907 diffract to 2.45â Å resolution and belong to space group C2 with unit-cell parameters a=136.1, b=78.5, c=103.4â Å, ß=118.8°, whereas Nb2919 crystals diffract to 2.15â Å resolution and belong to space group P43212 with unit-cell parameters a=b=62.7, c=167.2â Å.
Asunto(s)
Anticuerpos Antiprotozoarios/química , Antígenos de Protozoos/química , Plasmodium falciparum/química , Anticuerpos de Dominio Único/química , Secuencia de Aminoácidos , Animales , Anticuerpos Antiprotozoarios/genética , Anticuerpos Antiprotozoarios/aislamiento & purificación , Antígenos de Protozoos/inmunología , Sitios de Unión , Camélidos del Nuevo Mundo/inmunología , Cristalografía por Rayos X , Eritrocitos/parasitología , Escherichia coli/química , Escherichia coli/genética , Modelos Moleculares , Datos de Secuencia Molecular , Plasmodium falciparum/metabolismo , Estructura Secundaria de Proteína , Estructura Terciaria de Proteína , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Alineación de Secuencia , Homología de Secuencia de Aminoácido , Anticuerpos de Dominio Único/genética , Anticuerpos de Dominio Único/aislamiento & purificaciónRESUMEN
Here we present the preparation, biophysical characterization, and nuclear magnetic resonance (NMR) spectroscopy study of yeast cytochrome c peroxidase (CcP) constructs with enhanced solubility. Using a high-yield Escherichia coli expression system, we routinely produced uniformly labeled [(2)H,(13)C,(15)N]CcP samples with high levels of deuterium incorporation (96-99%) and good yields (30-60 mg of pure protein from 1 L of bacterial culture). In addition to simplifying the purification procedure, introduction of a His tag at either protein terminus dramatically increases its solubility, allowing preparation of concentrated, stable CcP samples required for multidimensional NMR spectroscopy. Using a range of biophysical techniques and X-ray crystallography, we demonstrate that the engineered His tags neither perturb the structure of the enzyme nor alter the heme environment or its reactivity toward known ligands. The His-tagged CcP constructs remain catalytically active yet exhibit differences in the interaction with cytochrome c, the physiological binding partner, most likely because of steric occlusion of the high-affinity binding site by the C-terminal His tag. We show that protein perdeuteration greatly increases the quality of the double- and triple-resonance NMR spectra, allowing nearly complete backbone resonance assignments and subsequent study of the CcP by heteronuclear NMR spectroscopy.
Asunto(s)
Citocromo-c Peroxidasa/química , Saccharomyces cerevisiae/enzimología , Secuencia de Aminoácidos , Dicroismo Circular , Clonación Molecular , Cristalografía por Rayos X , Citocromo-c Peroxidasa/genética , Citocromo-c Peroxidasa/aislamiento & purificación , Citocromo-c Peroxidasa/metabolismo , Citocromos c/metabolismo , Escherichia coli/genética , Expresión Génica , Cinética , Modelos Moleculares , Datos de Secuencia Molecular , Resonancia Magnética Nuclear Biomolecular , Unión Proteica , Saccharomyces cerevisiae/química , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/metabolismo , Solubilidad , Espectrometría de Masa por Ionización de ElectrosprayRESUMEN
Lying at the heart of many vital cellular processes such as photosynthesis and respiration, biological electron transfer (ET) is mediated by transient interactions among proteins that recognize multiple binding partners. Accurate description of the ET complexes - necessary for a comprehensive understanding of the cellular signaling and metabolism - is compounded by their short lifetimes and pronounced binding promiscuity. Here, we used a computational approach relying solely on the steric properties of the individual proteins to predict the ET properties of protein complexes constituting the functional interactome of the eukaryotic cytochrome c (Cc). Cc is a small, soluble, highly-conserved electron carrier protein that coordinates the electron flow among different redox partners. In eukaryotes, Cc is a key component of the mitochondrial respiratory chain, where it shuttles electrons between its reductase and oxidase, and an essential electron donor or acceptor in a number of other redox systems. Starting from the structures of individual proteins, we performed extensive conformational sampling of the ET-competent binding geometries, which allowed mapping out functional epitopes in the Cc complexes, estimating the upper limit of the ET rate in a given system, assessing ET properties of different binding stoichiometries, and gauging the effect of domain mobility on the intermolecular ET. The resulting picture of the Cc interactome 1) reveals that most ET-competent binding geometries are located in electrostatically favorable regions, 2) indicates that the ET can take place from more than one protein-protein orientation, and 3) suggests that protein dynamics within redox complexes, and not the electron tunneling event itself, is the rate-limiting step in the intermolecular ET. Further, we show that the functional epitope size correlates with the extent of dynamics in the Cc complexes and thus can be used as a diagnostic tool for protein mobility.
Asunto(s)
Citocromos c/metabolismo , Transporte de Electrón , Modelos Moleculares , Oxidación-Reducción , Unión Proteica , Transducción de SeñalRESUMEN
An efficient way to rapidly generate protein-ligand costructures based on solution-NMR using sparse NOE data combined with selective isotope labeling is presented. A docked model of the 27 kDa N-terminal ATPase domain of Hsp90 bound to a small molecule ligand was generated using only 21 intermolecular NOEs, which uniquely defined both the binding site and the orientation of the ligand. The approach can prove valuable for the early stages of fragment-based drug discovery.