G protein-coupled receptors (GPCRs) are involved in numerous physiological processes and are the most frequent targets of approved drugs. The explosion in the number of new 3D molecular structures of GPCRs (3D-GPCRome) during the last decade has greatly advanced the mechanistic understanding and drug design opportunities for this protein family. Molecular dynamics (MD) simulations have become a widely established technique to explore the conformational landscape of proteins at an atomic level. However, the analysis and visualization of MD simulations require efficient storage resources and specialized software. Here we present GPCRmd (http://gpcrmd.org/), an online platform that incorporates web-based visualization capabilities as well as a comprehensive and user-friendly analysis toolbox that allows scientists from different disciplines to visualize, analyse and share GPCR MD data.GPCRmd originates from a community-driven effort to create the first open, interactive, and standardized database of GPCR MD simulations.However, static high-resolution structures provide little information on the intrinsic 71 flexibility of GPCRs, a key aspect to fully understand their function. Important advances 72

Predicting the effect of single-point mutations on protein stability or protein-ligand binding is a major challenge in computational biology. Free energy calculations constitute the most rigorous approach to this problem, though the estimation of converged values for amino acid mutations is still challenging. To overcome this limitation, we developed a tailored protocol to calculate free energy shifts associated to single point mutations, which is now revised and implemented in an API framework and the graphic interface QGui for the MD software Q. We herein describe the QligFEP protocol and benchmark it in several model systems, optimizing a number of variables concerning sampling or the performance of Zwanzig's exponential formula and Bennet's acceptance ratio methods. QligFEP shows an excellent performance on estimating the hydration free energies of amino acid side chain mimics, included their charged analogs which were elusive in alternative FEP strategies. We next examined the performance on a protein-ligand binding problem of pharmaceutical relevance, the neuropeptide Y1 G protein-coupled receptor. Here, the calculations show very good agreement with the experimental effect of 16 mutations on the binding of antagonists BIBP3226, in line with our recent applications in this field. Finally, the characterization of 43 mutations of T4-lysozyme reveals the capacity of our protocol to assess variations of the thermal stability of proteins, achieving a similar performance to alternative FEP approaches. In summary, QresFEP is a robust, versatile and user-friendly computational FEP protocol to examine biochemical effects of single-point mutations with high accuracy.

Understanding the agonist-receptor interactions in the neuropeptide Y (NPY)/peptide YY (PYY) signaling system is fundamental for the design of novel modulators of appetite regulation. We report here the results of a multidisciplinary approach to elucidate the binding mode of the native peptide agonist PYY to the human Y receptor, based on computational modeling, peptide chemistry and in vitro pharmacological analyses. The preserved binding orientation proposed for full-length PYY and five analogs, truncated at the amino terminus, explains our pharmacological results where truncations of the N-terminal proline helix showed little effect on peptide affinity. This was followed by receptor mutagenesis to investigate the roles of several receptor positions suggested by the modeling. As a complement, PYY-(3-36) analogs were synthesized with modifications at different positions in the common PYY/NPY C-terminal fragment (TRQRY-amide). The results were assessed and interpreted by molecular dynamics and Free Energy Perturbation (FEP) simulations of selected mutants, providing a detailed map of the interactions of the PYY/NPY C-terminal fragment with the transmembrane cavity of the Y receptor. The amidated C-terminus would be stabilized by polar interactions with Gln288 and Tyr219, while Gln130 contributes to interactions with Q in the peptide and T is close to the tip of TM7 in the receptor. This leaves the core, -helix of the peptide exposed to make potential interactions with the extracellular loops. This model agrees with most experimental data available for the Y system and can be used as a basis for optimization of Y receptor agonists.

G protein-coupled receptors (GPCRs) are involved in numerous physiological processes and the most frequent targets of approved drugs. The striking explosion in the number of new 3D molecular structures of GPCRs (3D-GPCRome) during the last decade has greatly advanced the mechanistic understanding and drug design opportunities for this protein family. While experimentally-resolved structures undoubtedly provide valuable snapshots of specific GPCR conformational states, they give only limited information on their flexibility and dynamics associated with function.Molecular dynamics (MD) simulations have become a widely established technique to explore the conformational landscape of proteins at an atomic level. However, the analysis and visualization of MD simulations requires efficient storage resources and specialized software, hence limiting the dissemination of these data to specialists in the field. Here we present the GPCRmd, an online platform with web-based visualization capabilities and a comprehensive analysis toolbox that allows scientists from any discipline to visualize, share, and analyse GPCR MD data. We describe the GPCRmd in the context of a community-driven effort to create the first open, interactive, and standardized database of GPCR MD simulations. We demonstrate the power of this resource by performing comparative analyses of multiple GPCR simulations on two mechanisms critical to receptor function: internal water networks and sodium ion interaction.