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Structure-Based Consensus Scoring Scheme for Selecting Class A Aminergic GPCR Fragments

Aminergic G-protein coupled receptors (GPRCs) represent well-known targets of central nervous-system related diseases. In this study a structure-based consensus virtual screening scheme was developed for designing targeted fragment libraries against class A aminergic GPCRs. Nine representative aminergic GPCR structures were selected by first clustering available X-ray structures and then choosing the one in each cluster that performs best in self-docking calculations. A consensus scoring protocol was developed using known promiscuous aminergic ligands and decoys as a training set. The consensus score (FrACS-fragment aminergic consensus score) calculated for the optimized protein ensemble showed improved enrichments in most cases as compared to stand-alone structures. Retrospective validation was carried out on public screening data for aminergic targets (5-HT1 serotonin receptor, TA1 trace-amine receptor) showing 8-17-fold enrichments using an ensemble of aminergic receptor structures. The performance of the structure based FrACS in combination with our ligand-based prefilter (FrAGS) was investigated both in a retrospective validation on the ChEMBL database and in a prospective validation on an in-house fragment library. In prospective validation virtual fragment hits were tested on 5-HT6 serotonin receptors not involved in the development of FrACS. Six out of the 36 experimentally tested fragments exhibited remarkable antagonist efficacies, and 4 showed IC50 values in the low micromolar or submicromolar range in a cell-based assay. Both retrospective and prospective validations revealed that the methodology is suitable for designing focused class A GPCR fragment libraries from large screening decks, commercial compound collections, or virtual databases.

Combination of 2D/3D Ligand-Based Similarity Search in Rapid Virtual Screening from Multimillion Compound Repositories. Selection and Biological Evaluation of Potential PDE4 and PDE5 Inhibitors

Rapid in silico selection of target focused libraries from commercial repositories is an attractive and cost effective approach. If structures of active compounds are available rapid 2D similarity search can be performed on multimillion compound databases but the generated library requires further focusing by various 2D/3D chemoinformatics tools. We report here a combination of the 2D approach with a ligand-based 3D method (Screen3D) which applies flexible matching to align reference and target compounds in a dynamic manner and thus to assess their structural and conformational similarity. In the first case study we compared the 2D and 3D similarity scores on an existing dataset derived from the biological evaluation of a PDE5 focused library. Based on the obtained similarity metrices a fusion score was proposed. The fusion score was applied to refine the 2D similarity search in a second case study where we aimed at selecting and evaluating a PDE4B focused library. The application of this fused 2D/3D similarity measure led to an increase of the hit rate from 8.5% (1st round, 47% inhibition at 10 µM) to 28.5% (2nd round at 50% inhibition at 10 µM) and the best two hits had 53 nM inhibitory activities.

Combining 2D and 3D in silico methods for rapid selection of potential PDE5 inhibitors from multimillion compounds’ repositories: biological evaluation

Rapid in silico selection of target focused libraries from commercial repositories is an attractive and cost-effective approach when starting new drug discovery projects. If structures of active compounds are available rapid 2D similarity search can be performed on multimillion compounds’ databases. This in silico approach can be combined with physico-chemical parameter filtering based on the property space of the active compounds and 3D virtual screening if the structure of the target protein is available. A multi-step virtual screening procedure was developed and applied to select potential phosphodiesterase 5 (PDE5) inhibitors in real time. The combined 2D/3D in silico method resulted in the identification of 14 novel PDE5 inhibitors with <1 μMIC50 values and the hit rate in the second in silico selection and in vitro screening round exceeded the 20%.

Combination of Pharmacophore Matching, 2D Similarity Search, and In Vitro Biological Assays in the Selection of Potential 5-HT6 Antagonists from Large Commercial Repositories

Rapid in silico selection of target‐focused libraries from commercial repositories is an attractive and cost‐effective approach. If structures of active compounds are available, rapid 2D similarity search can be performed on multimillion compound databases, but the generated library requires further focusing. We report here a combination of the 2D approach with pharmacophore matching which was used for selecting 5‐HT6 antagonists. In the first screening round, 12 compounds showed >85% antagonist efficacy of the 91 screened. For the second‐round (hit validation) screening phase, pharmacophore models were built, applied, and compared with the routine 2D similarity search. Three pharmacophore models were created based on the structure of the reference compounds and the first‐round hit compounds. The pharmacophore search resulted in a high hit rate (40%) and led to novel chemotypes, while 2D similarity search had slightly better hit rate (51%), but lacking the novelty. To demonstrate the power of the virtual screening cascade, ligand efficiency indices were also calculated and their steady improvement was confirmed.

The Initiation Complexes of the Classical and Lectin Pathways

Various antigen structures initiate the classical and the lectin pathways of complement activation. Multidomain modular proteases (C1r, C1s and MASPs) are involved in the initiation complexes of both pathways. Despite the identical domain organization of these serine proteases there are differences in their specificities and functions. A comparative analysis is given on the similarities and differences of the mechanism of action of these proteases, with emphasize on structural aspects. Recent structural and functional data underline the significance of molecular dynamics in the activation process of both C1 and MBL/MASPs. While the role of MASP-2 in the lectin pathway is supported by increasing number of evidence, the same can not be said about MASP-1 and MASP-3. The role of the initiation complexes in pathological processes such as inflammation and subsequent repair processes, apoptosis, susceptibility to infectious diseases etc. is also reviewed. C1 inhibitor is essential in regulating both pathways. This serpin interacts with several serine proteases including C1r, C1s and MASPs. C1 inhibitor deficiency related diseases, and C1 inhibitor as a therapeutic agent is also discussed.

Monoclonal antibody proteomics: Use of antibody mimotope displaying phages and the relevant synthetic peptides for mAb scouting

Monoclonal antibody proteomics uses nascent libraries or cloned (Plasmascan™, QuantiPlasma™) libraries of mAbs that react with individual epitopes of proteins in the human plasma. At the initial phase of library creation, cognate protein antigen and the epitope interacting with the antibodies are not known. Scouting for monoclonal antibodies (mAbs) with the best binding characteristics is of high importance for mAb based biomarker assay development. However, in the absence of the identity of the cognate antigen the task represents a challenge. We combined phage display, and surface plasmon resonance (Biacore) experiments to test whether specific phages and the respective mimotope peptides obtained from large scale studies are applicable to determine key features of antibodies for scouting. We show here that mAb captured phage-mimotope heterogeneity that is the diversity of the selected peptide sequences, is inversely correlated with an important binding descriptor; the off-rate of the antibodies and that represents clues for driving the selection of useful mAbs for biomarker assay development. Carefully chosen synthetic mimotope peptides are suitable for specificity testing in competitive assays using the target proteome, in our case the human plasma.

C1-inhibitor structure reveals a novel mechanism of heparin potentiation

24 European Crystallographic Meeting, ECM24, Marrakech, 2007 Page s129 Acta Cryst. (2007). A63, s129 motif, while the C-terminal domain shows a typical restriction endonuclease fold. By structural comparison and mutational analysis we showed that the active site of SdaI is located at the C-terminal domain and exhibits a new variation of the canonical PD...(D/E)XK active site motif. Mutational analysis of the residues from the predicted recognition helix of the wHTH motif suggests that SdaI determinants of sequence specificity are clustered at the N-terminal domain. The modular architecture of SdaI, wherein one domain mediates DNA binding while the other domain is predicted to catalyze hydrolysis, distinguishes SdaI from the previously characterized restriction enzymes interacting with symmetric recognition sequences.