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Positive allosteric modulators (PAMs) of metabotropic glutamate receptor type 5 (mGluR 5 ), a prototypical class C G protein-coupled receptor (GPCR), have shown therapeutic potential for various neurological disorders. Understanding the allosteric activation mechanism is essential for the rational design of mGluR 5 PAMs. We studied the actions of positive and negative allosteric modulators within the transmembrane domain of mGluR 5 , using enhance-sampling all-atom molecular dynamics simulations. We found dual binding modes of the PAM, associated with distinct shapes of the allosteric pocket. The negative allosteric modulators, in contrast, showed only one binding mode. The simulations revealed the mechanism by which the PAM activated the receptor, in the absence of the orthosteric agonist (the so-called allosteric agonism). The mechanism relied on dynamic communications between amino-acid motifs that are highly conserved across class C GPCRs. The findings may guide structure-based design and virtual screening of allosteric modulators for mGluR 5 as well as for other class C GPCRs.

A replica-exchange protocol remarkably enhances the sampling of the activation dynamics of the neurotensin receptor type 1, a G protein-coupled receptor (GPCR) and important drug target. Our work highlights the dynamic communication between conformational changes of the agonist and the G protein-binding site, via contraction-oscillation of the orthosteric pocket. It also gives insights into the mechanism by which certain mutations diminish or stimulate activation. The replica-exchange protocol effectively enhances barrier crossing where standard brute-force molecular dynamics simulations fail. It is readily applicable to other GPCRs and represents a promising approach for virtual ligand screening, using the typical features of receptor activation as a benchmark.

Quercetin, one of the most representative flavonoid compounds, is involved in antiradical, antioxidant, and prooxidant biological processes. Despite a constant increase of knowledge on both positive and negative activities of quercetin, it is unclear which activated form (quinone, semiquinone, or deprotonated) actually plays a role in each of these processes. Structural, electronic, and energetic characteristics of quercetin, as well as the influence of a copper ion on all of these parameters, are studied by means of quantum chemical electronic structure calculations. Introduction of thermodynamic cycles together with the role of coreactive compounds, such as reactive oxygen species, gives a glimpse of the most probable reaction schemes. Such a theoretical approach provides another hint to clarify which reaction is likely to occur within the broad range of quercetin biological activities.