Site-directed mutagenesis data is commonly used to validate and rationalize receptor homology models and ligand docking poses. Exploring allosteric modulators (AM) of class C GPCRs, we collected an extensive set of 1531 single point mutations on 75 allosteric modulators from 35 publications and mapped these on the recently published mGlu crystal structures. The analysis shows that class C negative and positive AMs bind to identical binding sites and that the available structural templates that were crystallized in complex with negative AMs can very likely serve as templates for positive AM studies. Furthermore, the structural mapping paints a clear picture of which observed mutant effects are direct and which are indirect while identification of the binding site residues show that the allosteric ligand receptor sites group according to the classical receptor families. Additionally, we applied the mutagenesis data to validate docking binding poses of selective mGlu AMs to rationalize ligand selectivity and identify receptor selectivity hotspots for future mutagenesis studies. This combined structural, mutagenesis and AM data lays a foundation for rational structure-based design of novel modulators or to design new mutagenesis experiments where data is still insufficient.

To ease the time-consuming and tedious work of organising and analysing the huge number of data points in research projects we have added the Mutation browser to the G Protein-Coupled Receptor Database, GPCRdb. With this tool, annotated mutagenesis data can quickly be filtered according to target protein, receptor position, ligand and effect on ligand affinity/function. Furthermore, positions of interest can be mapped on receptor helix-box and snake plot diagrams to delineate binding sites and identify interaction hotspots. Additionally, we have very recently developed a new Mutant design tool to aid in the process of designing new site directed mutagenesis experiment, which are now available in GPCRdb. Here users can upload a protein-ligand complex to received a list of suggested mutations based on an analysis of the interactions between ligand and protein and are, thus, directed towards affecting affinity and function of the ligand of choice. Alternatively, a receptor target name can be specified to receive a list of suggested mutations based on protein-ligand interactions in crystal structures and existing mutagenesis experiments within the same GPCR class.