RESUMEN
MUS81 is a structure-selective endonuclease that cleaves various branched DNA structures arising from natural physiological processes such as homologous recombination and mitosis. Due to this, MUS81 is able to relieve replication stress, and its function has been reported to be critical to the survival of many cancers, particularly those with dysfunctional DNA-repair machinery. There is therefore interest in MUS81 as a cancer drug target, yet there are currently few small molecule inhibitors of this enzyme reported, and no liganded crystal structures are available to guide hit optimization. Here we report the fragment-based discovery of novel small molecule MUS81 inhibitors with sub-µM biochemical activity. These inhibitors were used to develop a novel crystal system, providing the first structural insight into the inhibition of MUS81 with small molecules.
RESUMEN
Bfl-1 is overexpressed in both hematological and solid tumors; therefore, inhibitors of Bfl-1 are highly desirable. A DNA-encoded chemical library (DEL) screen against Bfl-1 identified the first known reversible covalent small-molecule ligand for Bfl-1. The binding was validated through biophysical and biochemical techniques, which confirmed the reversible covalent mechanism of action and pointed to binding through Cys55. This represented the first identification of a cyano-acrylamide reversible covalent compound from a DEL screen and highlights further opportunities for covalent drug discovery through DEL screening. A 10-fold improvement in potency was achieved through a systematic SAR exploration of the hit. The more potent analogue compound 13 was successfully cocrystallized in Bfl-1, revealing the binding mode and providing further evidence of a covalent interaction with Cys55.
RESUMEN
Covalent hit identification is a viable approach to identify chemical starting points against difficult-to-drug targets. While most researchers screen libraries of <2k electrophilic fragments, focusing on lead-like compounds can be advantageous in terms of finding hits with improved affinity and with a better chance of identifying cryptic pockets. However, due to the increased molecular complexity, larger numbers of compounds (>10k) are desirable to ensure adequate coverage of chemical space. Herein, the approach taken to build a library of 12k covalent lead-like compounds is reported, utilizing legacy compounds, robust library chemistry, and acquisitions. The lead-like covalent library was screened against the antiapoptotic protein Bfl-1, and six promising hits that displaced the BIM peptide from the PPI interface were identified. Intriguingly, X-ray crystallography of lead-like compound 8 showed that it binds to a previously unobserved conformation of the Bfl-1 protein and is an ideal starting point for the optimization of Bfl-1 inhibitors.
Asunto(s)
Cisteína , Diseño de Fármacos , Bibliotecas de Moléculas Pequeñas , Bibliotecas de Moléculas Pequeñas/química , Bibliotecas de Moléculas Pequeñas/farmacología , Cristalografía por Rayos X , Cisteína/química , Humanos , Proteínas Proto-Oncogénicas c-bcl-2/antagonistas & inhibidores , Proteínas Proto-Oncogénicas c-bcl-2/química , Proteínas Proto-Oncogénicas c-bcl-2/metabolismo , Relación Estructura-Actividad , Modelos Moleculares , Antígenos de Histocompatibilidad MenorRESUMEN
Dysregulation of histone methyl transferase nuclear receptor-binding SET domain 2 (NSD2) has been implicated in several hematological and solid malignancies. NSD2 is a large multidomain protein that carries histone writing and histone reading functions. To date, identifying inhibitors of the enzymatic activity of NSD2 has proven challenging in terms of potency and SET domain selectivity. Inhibition of the NSD2-PWWP1 domain using small molecules has been considered as an alternative approach to reduce NSD2-unregulated activity. In this article, we present novel computational chemistry approaches, encompassing free energy perturbation coupled to machine learning (FEP/ML) models as well as virtual screening (VS) activities, to identify high-affinity NSD2 PWWP1 binders. Through these activities, we have identified the most potent NSD2-PWWP1 binder reported so far in the literature: compound 34 (pIC50 = 8.2). The compounds identified herein represent useful tools for studying the role of PWWP1 domains for inhibition of human NSD2.
Asunto(s)
Diseño de Fármacos , N-Metiltransferasa de Histona-Lisina , N-Metiltransferasa de Histona-Lisina/antagonistas & inhibidores , N-Metiltransferasa de Histona-Lisina/metabolismo , N-Metiltransferasa de Histona-Lisina/química , Ligandos , Humanos , Proteínas Represoras/antagonistas & inhibidores , Proteínas Represoras/química , Proteínas Represoras/metabolismo , Relación Estructura-Actividad , Aprendizaje Automático , Modelos Moleculares , Dominios ProteicosRESUMEN
Fragment based drug discovery is a critical part of the lead generation toolbox and relies heavily on a readily available, high quality fragment library. Over years of use, the AstraZeneca fragment set had become partially depleted and instances of compound deterioration had been found. It was recognised that a redevelopment was required. This provided an opportunity to evolve our screening sets strategy, whilst ensuring that the quality of the fragment set met the robust requirements of fragment screening campaigns. In this communication we share the strategy employed, in particular highlighting two aspects of our approach that we believe others in the community would benefit from, namely that; (i) fragments were selected with input from Medicinal Chemists at an early stage, and (ii) the library was arranged in a layered format to ensure maximum flexibility on a per target basis.
RESUMEN
The bromodomain and extra-terminal (BET) protein BRD4 regulates gene expression via recruitment of transcriptional regulatory complexes to acetylated chromatin. Like other BET proteins, BRD4 contains two bromodomains, BD1 and BD2, that can interact cooperatively with target proteins and designed ligands, with important implications for drug discovery. Here, we used nuclear magnetic resonance (NMR) spectroscopy to study the dynamics and interactions of the isolated bromodomains, as well as the tandem construct including both domains and the intervening linker, and investigated the effects of binding a tetra-acetylated peptide corresponding to the tail of histone 4. The peptide affinity is lower for both domains in the tandem construct than for the isolated domains. Using 15N spin relaxation, we determined the global rotational correlation times and residue-specific order parameters for BD1 and BD2. Isolated BD1 is monomeric in the apo state but apparently dimerizes upon binding the tetra-acetylated peptide. Isolated BD2 partially dimerizes in both the apo and peptide-bound states. The backbone order parameters reveal marked differences between BD1 and BD2, primarily in the acetyl-lysine binding site where the ZA loop is more flexible in BD2. Peptide binding reduces the order parameters of the ZA loop in BD1 and the ZA and BC loops in BD2. The AB loop, located distally from the binding site, shows variable dynamics that reflect the different dimerization propensities of the domains. These results provide a basis for understanding target recognition by BRD4.
Asunto(s)
Histonas , Proteínas Nucleares , Histonas/metabolismo , Proteínas Nucleares/metabolismo , Factores de Transcripción/química , Sitios de Unión , Péptidos/metabolismo , Proteínas de Ciclo Celular/metabolismoRESUMEN
Structure-based drug discovery (SBDD) largely relies on structural information from X-ray crystallography because traditional NMR structure calculation methods are too time consuming to be aligned with typical drug discovery timelines. The recently developed NMR molecular replacement (NMR2) method dramatically reduces the time needed to generate ligand-protein complex structures using published structures (apo or holo) of the target protein and treating all observed NOEs as ambiguous restraints, bypassing the laborious process of obtaining sequence-specific resonance assignments for the protein target. We apply this method to two therapeutic targets, the bromodomain of TRIM24 and the second bromodomain of BRD4. We show that the NMR2 methodology can guide SBDD by rationalizing the observed SAR. We also demonstrate that new types of restraints and selective methyl labeling have the potential to dramatically reduce "time to structure" and extend the method to targets beyond the reach of traditional NMR structure elucidation.
Asunto(s)
Proteínas Nucleares , Factores de Transcripción , Cristalografía por Rayos X , Espectroscopía de Resonancia Magnética , Proteínas Nucleares/metabolismo , Unión Proteica , Dominios Proteicos , Factores de Transcripción/metabolismoRESUMEN
ATAD2 is an epigenetic bromodomain-containing target which is overexpressed in many cancers and has been suggested as a potential oncology target. While several small molecule inhibitors have been described in the literature, their cellular activity has proved to be underwhelming. In this work, we describe the identification of a novel series of ATAD2 inhibitors by high throughput screening, confirmation of the bromodomain region as the site of action, and the optimization campaign undertaken to improve the potency, selectivity, and permeability of the initial hit. The result is compound 5 (AZ13824374), a highly potent and selective ATAD2 inhibitor which shows cellular target engagement and antiproliferative activity in a range of breast cancer models.
Asunto(s)
ATPasas Asociadas con Actividades Celulares Diversas/antagonistas & inhibidores , Antineoplásicos/síntesis química , Antineoplásicos/farmacología , Neoplasias de la Mama/tratamiento farmacológico , Proteínas de Unión al ADN/antagonistas & inhibidores , Línea Celular Tumoral , Cristalografía por Rayos X , Descubrimiento de Drogas , Ensayos de Selección de Medicamentos Antitumorales , Femenino , Humanos , Modelos Moleculares , Bibliotecas de Moléculas Pequeñas , Relación Estructura-Actividad , Especificidad por Sustrato , Ensayo de Tumor de Célula MadreRESUMEN
Biophysical methods such as mass spectrometry, surface plasmon resonance, nuclear magnetic resonance, and both differential scanning isothermal titration calorimetry are now well established as key components of the early drug discovery process. These approaches are used successfully for a range of activities, including assay development, primary screening, hit confirmation and detailed mechanistic characterisation of compound binding. Matching the speed, sensitivity and information content of the various techniques to the generation of critical data and information required at each phase of the drug discovery process has been key. This review describes the framework by which these methods have been applied in the drug discovery process and provides case studies to exemplify the impact.
RESUMEN
Aberrant NSD2 methyltransferase activity is implicated as the oncogenic driver in multiple myeloma, suggesting opportunities for novel therapeutic intervention. The methyltransferase activity of NSD2 resides in its catalytic SET domain, which is conserved among most lysine methyltransferases. Here we report the backbone [Formula: see text], N, C[Formula: see text], [Formula: see text] and side-chain [Formula: see text] assignments of a 25 kDa NSD2 SET domain construct, spanning residues 991-1203. A chemical shift analysis of C[Formula: see text], [Formula: see text] and [Formula: see text] resonances predicts a secondary structural pattern that is in agreement with homology models.
Asunto(s)
N-Metiltransferasa de Histona-Lisina/química , Resonancia Magnética Nuclear Biomolecular , Proteínas Represoras/química , Humanos , Dominios Proteicos , Estructura Secundaria de ProteínaRESUMEN
Bromodomain and extra-terminal (BET) family of proteins are one of the major readers of epigenetic marks and an important target class in oncology and other disease areas. The importance of the BET family of proteins is manifested by the explosion in the number of inhibitors against these targets that have successfully entered clinical trials. One important BET family member is bromodomain containing protein 4 (BRD4). Structural and biophysical studies of BRD4 are complicated by its tertiary-structure consisting of two bromodomains connected by a flexible inter-domain linker of approximately 180 amino acids. A detailed understanding of the interplay of these bromodomains will be key to rational drug design in BRD4, yet there are no reported three-dimensional structures of the multi-domain BRD4 and NMR studies of the tandem domain are hampered by the size of the protein. Here, we present a method for rapid Sortase A-mediated segmental labelling of the individual bromodomains of BRD4 that provides a powerful strategy that will enable NMR studies of ligand-bromodomain interactions with atomic detail. In our labelling strategy, we have used U-[2H,15N]-isotope labelling on the C-terminal bromodomain with selective introduction of 13CH3 methyl groups on Ile (δ1), Val and Leu, whereas the N-terminal bromodomain remained unlabelled. This labelling scheme resulted in significantly simplified NMR spectra and will allow for high-resolution interaction, structure and dynamics studies in the presence of ligands.
Asunto(s)
Aminoaciltransferasas , Proteínas Bacterianas , Cisteína Endopeptidasas , Marcaje Isotópico/métodos , Proteínas Nucleares/química , Factores de Transcripción/química , Secuencia de Aminoácidos , Fenómenos Biofísicos , Proteínas de Ciclo Celular , Humanos , Modelos Moleculares , Resonancia Magnética Nuclear Biomolecular , Proteínas Nucleares/genética , Dominios Proteicos , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Factores de Transcripción/genéticaRESUMEN
Plant homeodomains (PHD) and Bromo domains are both chromatin reader domains that recognise histone methylation degree and acetylation state, respectively. The tripartite motif protein TRIM24 is a multidomain protein carrying a PHD-Bromo motif at its C-terminus, through which it is able to bind to histone 3 (H3) N-terminal tails with a specific modification pattern, namely unmethylated at K4 and acetylated at K23 (H3-K4me0K23ac). Here we report the 1H, 13C and 15N backbone resonance assignment of this 23 kDa motif, which we have obtained by heteronuclear multidimensional NMR spectroscopy. Furthermore we show that the secondary Cα and Cß chemical shifts are in good agreement with a previously published crystal structure.
Asunto(s)
Cromatina/química , Resonancia Magnética Nuclear Biomolecular , Humanos , Dominios Proteicos , Estructura Secundaria de ProteínaRESUMEN
For typical globular proteins, contacts involving aromatic side chains would constitute the largest number of distance constraints that could be used to define the structure of proteins and protein complexes based on NOE contacts. However, the (1)H NMR signals of aromatic side chains are often heavily overlapped, which hampers extensive use of aromatic NOE cross peaks. Some of this overlap can be overcome by recording (13)C-dispersed NOESY spectra. However, the resolution in the carbon dimension is rather low due to the narrow dispersion of the carbon signals, large one-bond carbon-carbon (C-C) couplings, and line broadening due to chemical shift anisotropy (CSA). Although it has been noted that the CSA of aromatic carbons could be used in TROSY experiments for enhancing resolution, this has not been used much in practice because of complications arising from large aromatic one-bond C-C couplings, and 3D or 4D carbon dispersed NOESY are typically recorded at low resolution hampering straightforward peak assignments. Here we show that the aromatic TROSY effect can optimally be used when employing alternate (13)C labeling using 2-(13)C glycerol, 2-(13)C pyruvate, or 3-(13)C pyruvate as the carbon source. With the elimination of the strong one-bond C-C coupling, the TROSY effect can easily be exploited. We show that (1)H-(13)C TROSY spectra of alternately (13)C labeled samples can be recorded at high resolution, and we employ 3D NOESY aromatic-TROSY spectra to obtain valuable intramolecular and intermolecular cross peaks on a protein complex.
Asunto(s)
Aminoácidos Aromáticos/química , Isótopos de Carbono/química , Resonancia Magnética Nuclear Biomolecular/métodos , Proteínas/químicaRESUMEN
Recognition of the proper start codon on mRNAs is essential for protein synthesis, which requires scanning and involves eukaryotic initiation factors (eIFs) eIF1, eIF1A, eIF2, and eIF5. The carboxyl terminal domain (CTD) of eIF5 stimulates 43S preinitiation complex (PIC) assembly; however, its precise role in scanning and start codon selection has remained unknown. Using nuclear magnetic resonance (NMR) spectroscopy, we identified the binding sites of eIF1 and eIF2ß on eIF5-CTD and found that they partially overlapped. Mutating select eIF5 residues in the common interface specifically disrupts interaction with both factors. Genetic and biochemical evidence indicates that these eIF5-CTD mutations impair start codon recognition and impede eIF1 release from the PIC by abrogating eIF5-CTD binding to eIF2ß. This study provides mechanistic insight into the role of eIF5-CTD's dynamic interplay with eIF1 and eIF2ß in switching PICs from an open to a closed state at start codons.
Asunto(s)
Codón Iniciador/metabolismo , Factor 1 Eucariótico de Iniciación/metabolismo , Factor 2 Eucariótico de Iniciación/metabolismo , Factor 5 Eucariótico de Iniciación/química , Factor 5 Eucariótico de Iniciación/metabolismo , Secuencia de Aminoácidos , Sustitución de Aminoácidos/genética , Sitios de Unión , Secuencia Conservada , Epítopos/metabolismo , Factor 1 Eucariótico de Iniciación/química , Factor 2 Eucariótico de Iniciación/química , Evolución Molecular , Eliminación de Gen , Prueba de Complementación Genética , Humanos , Cinética , Lisina/metabolismo , Espectroscopía de Resonancia Magnética , Modelos Moleculares , Datos de Secuencia Molecular , Proteínas Mutantes/química , Proteínas Mutantes/metabolismo , Fenotipo , Unión Proteica , Estructura Terciaria de Proteína , Saccharomyces cerevisiae/citología , Saccharomyces cerevisiae/metabolismo , Dispersión del Ángulo Pequeño , Relación Estructura-Actividad , Difracción de Rayos XRESUMEN
The fast Fourier transformation has been the gold standard for transforming data from time to frequency domain in many spectroscopic methods, including NMR. While reliable, it has as a drawback that it requires a grid of uniformly sampled data points. This needs very long measuring times for sampling in multidimensional experiments in all indirect dimensions uniformly and even does not allow reaching optimal evolution times that would match the resolution power of modern high-field instruments. Thus, many alternative sampling and transformation schemes have been proposed. Their common challenges are the suppression of the artifacts due to the non-uniformity of the sampling schedules, the preservation of the relative signal amplitudes, and the computing time needed for spectra reconstruction. Here we present a fast implementation of the Iterative Soft Thresholding approach (istHMS) that can reconstruct high-resolution non-uniformly sampled NMR data up to four dimensions within a few hours and make routine reconstruction of high-resolution NUS 3D and 4D spectra convenient. We include a graphical user interface for generating sampling schedules with the Poisson-Gap method and an estimation of optimal evolution times based on molecular properties. The performance of the approach is demonstrated with the reconstruction of non-uniformly sampled medium and high-resolution 3D and 4D protein spectra acquired with sampling densities as low as 0.8%. The method presented here facilitates acquisition, reconstruction and use of multidimensional NMR spectra at otherwise unreachable spectral resolution in indirect dimensions.
Asunto(s)
Resonancia Magnética Nuclear Biomolecular/métodos , Modelos Moleculares , Proteínas/química , Interfaz Usuario-ComputadorRESUMEN
Experiments detecting low gyromagnetic nuclei have recently been proposed to utilize the relatively slow relaxation properties of these nuclei in comparison to (1)H. Here we present a new type of (15)N direct-detection experiment. Like the previously proposed CaN experiment (Takeuchi et al. in J Biomol NMR 47:271-282, 2010), the hCaN experiment described here sequentially connects amide (15)N resonances, but utilizes the initial high polarization and the faster recovery of the (1)H nucleus to shorten the recycling delay. This allows recording 2D (15)N-detected NMR experiments on proteins within a few hours, while still obtaining superior resolution for (13)C and (15)N, establishing sequential assignments through prolines, and at conditions where amide protons exchange rapidly. The experiments are demonstrated on various biomolecules, including the small globular protein GB1, the 22 kDa HEAT2 domain of eIF4G, and an unstructured polypeptide fragment of NFAT1, which contains many SerPro sequence repeats.
Asunto(s)
Isótopos de Nitrógeno , Resonancia Magnética Nuclear Biomolecular/métodos , Proteínas/química , Factor 4G Eucariótico de Iniciación/química , Humanos , Factores de Transcripción NFATC/química , Conformación Proteica , Receptores de GABA-B/químicaRESUMEN
The human Mediator coactivator complex interacts with many transcriptional activators and facilitates recruitment of RNA polymerase II to promote target gene transcription. The MED25 subunit is a critical target of the potent herpes simplex 1 viral transcriptional activator VP16. Here we determine the solution structure of the MED25 VP16-binding domain (VBD) and define its binding site for the N-terminal portion of the VP16 transactivation domain (TADn). A hydrophobic furrow, formed by a ß-barrel and two α-helices in MED25 VBD, interacts tightly with VP16 TADn. Mutations in this furrow prevent binding of VP16 TAD to MED25 VBD and interfere with the ability of overexpressed MED25 VBD to inhibit VP16-dependent transcriptional activation in vivo. This detailed molecular understanding of transactivation by the benchmark activator VP16 could provide important insights into viral and cellular gene activation mechanisms.
Asunto(s)
Proteína Vmw65 de Virus del Herpes Simple/química , Complejo Mediador/química , Proteína Vmw65 de Virus del Herpes Simple/genética , Humanos , Complejo Mediador/genética , Mutación , Resonancia Magnética Nuclear Biomolecular , Mutación Puntual , Conformación ProteicaRESUMEN
The cysteine-rich N and C-terminal domains of minicollagen-1 from Hydra nematocysts fold with excesses of oxidized/reduced glutathione (10:1) into globular structures with distinct cystine frameworks despite their identical cysteine sequence pattern. An additional main difference is the cis conformation of a conserved proline residue in the N-terminal and the trans conformation of this residue in the C-terminal domain. Comparative analysis of the oxidative folding revealed for the C-terminal domain a fast and highly cooperative formation of a single disulfide isomer. Conversely, oxidation of the N-terminal domain proceeds mainly via an intermediate that results from the fast quasi-stochastic disulfide formation according to the proximity rule. The rate of conversion of the bead-like isomer into the globular end-product is largely dominated by the trans-to-cis isomerization of the critical proline residue as well assessed by its replacement with (4R)- and (4S)-fluoroproline known to exhibit distinct propensities for the trans and cis conformation, respectively. Independently, whether the trans or cis conformation is favored by these substitutions, both analogues retain sufficient sequence-encoded information to fold almost quantitatively into the identical cystine framework and thus spatial structure of the parent peptide with the critical proline residue as cis isomer, but at rates significantly lower for the (4R) than for the (4S)-fluoroproline analogue. Correspondingly, other sequence-encoded structural elements have to act as a driving force for these unidirectional folding pathways despite the rather simple sequence composition consisting only of aliphatic residues, some proline and only one aromatic residue (tyrosine) in the core parts of the C and N-terminal domains. The two cysteine-rich domains of minicollagen-1 may well represent ideal targets for ab initio structure calculations in order to learn more about the elementary information encoded in such primordial molecules.
Asunto(s)
Colágeno/química , Colágeno/metabolismo , Cisteína/metabolismo , Fragmentos de Péptidos/química , Fragmentos de Péptidos/metabolismo , Prolina/metabolismo , Pliegue de Proteína , Secuencia de Aminoácidos , Animales , Cromatografía Líquida de Alta Presión , Colágeno/genética , Cisteína/genética , Hydra/química , Hydra/genética , Hydra/metabolismo , Cinética , Espectroscopía de Resonancia Magnética , Modelos Moleculares , Datos de Secuencia Molecular , Oxidación-Reducción , Fragmentos de Péptidos/genética , Prolina/análogos & derivados , Prolina/genética , Estructura Terciaria de ProteínaRESUMEN
Combining an azobenzene chromophore with the bis-cysteinyl active-site sequence of the protein disulfide isomerase (PDI) we constructed a simple but promising model for allosteric conformational rearrangements. Paralleling cellular signaling events, an external trigger, here absorption of a photon, leads to a structural change in one part of the molecule, namely the azobenzene-based chromophore. The change in geometry translates to the effector site, in our case the peptide sequence, where it modifies covalent and nonbonded interactions and thus leads to a conformational rearrangement. NMR spectroscopy showed that the trans-azo and cis-azo isomer of the cyclic PDI peptide exhibit different, but well-defined structures when the two cystine residues form a disulfide bridge. Without this intramolecular cross-link conformationally more variable structural ensembles are obtained that again differ for the two isomeric states. Ultrafast UV/Vis spectroscopy confirmed that the rapid isomerization of azobenzene is not significantly slowed down when incorporated into the cyclic peptides, although the amplitudes of ballistic and diffusive pathways are changed. The observation that most of the energy of an absorbed photon is dissipated to the solvent in the first few picoseconds when the actual azo-isomerization takes place is important. The conformational rearrangement is weakly driven due to the absence of appreciable excess energy and can be described as biased diffusion similar to natural processes.
Asunto(s)
Luz , Modelos Químicos , Modelos Moleculares , Proteína Disulfuro Isomerasas/química , Proteína Disulfuro Isomerasas/efectos de la radiación , Simulación por Computador , Relación Dosis-Respuesta en la Radiación , Activación Enzimática/efectos de la radiación , Péptidos/química , Péptidos/efectos de la radiación , Conformación Proteica/efectos de la radiación , Dosis de RadiaciónRESUMEN
In a comparison of structure calculation protocols we clearly demonstrate the need for generating independent starting structures, which is for peptides most efficiently achieved by distance geometry (DG) methods. Our test set consisted of 20 peptides with 7-9 amino acid residues additionally constrained by backbone cyclization and/or the presence of a disulfide bridge. Small peptides usually adopt defined conformational properties only upon introduction of additional constraints, such as cyclization. Therefore, we believe the results of our comparison to be applicable to a large and important class of molecules. The problems associated with the use of restrained molecular dynamics (MD) for conformational searching in the context of structure calculation consist in energy barriers that derive mainly but not exclusively from the experimental NOE constraints. A valid alternative to the DG approach, although for peptides computationally less efficient, is MD simulated annealing starting from random structures as commonly performed in the protein structure calculation from NMR data. As a consequence of our study it must be expected that a considerable fraction of published peptide structures are artificially well-defined or even wrong. Given the relevance of peptide studies for both drug development and protein folding we regard it highly important that structure calculations of peptides are performed with more consideration.