Structural and energetic insights into the selective interactions of monoacylglycerol lipase with its natural substrate and small-molecule inhibitors

The monoacylglycerol lipase (MAGL) regulates 2-arachidonoyl glycerol (2-AG) level in the endocannabinoid system (ECS), which is implicated in a number of severe diseases such as cancer and Alzheimer's disease. However, most existing MAGL inhibitors also show additional inhibitory effects on fatty acid amide hydrolase (FAAH), another member of the ECS that degrades the 2-AG analog N-arachidonoyl ethanolamine. Understanding of molecular mechanism and biological implication underlying the specific interactions in MAGL-ligand recognition is thus fundamentally important for the rational design of selective MAGL inhibitors. In the current study, the structural basis and energetic property regarding the binding of several MAGL inhibitors as well as its substrate 2-AG to both the MAGL and FAAH are investigated systematically by integrating molecular docking, quantum mechanics/molecular mechanics analysis, and Poisson-Boltzmann/surface area solvent model. In addition, a novel quantitative structure-selectivity relationship method is proposed to help in the explanation and prediction of inhibitor selectivity between MAGL and FAAH. It is suggested that the selectivity is primarily determined by the size, topology, and property of the rear moiety of inhibitor compounds; a bulky, bifurcated rear is the prerequisite for a inhibitor to have high selectivity for MAGL over FAAH, whereas those dual-type MAGL-FAAH inhibitors should possess a small, rear moiety-the ideal choice is a single aromatic branch occupying this position.