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Crystal Structure of MGL

Background

Metabolic Role

Component of Endocannabinoid System

Structure

Catalytic triad

MGL has a classic catalytic triad that contains Ser-His-Asp (figure 1). The triad was found using site-directed mutagenesis and this experiment confirmed that these amino acid residues are catalytically essential. The catalytic triad is located in the binding pocket buried at the bottom of it in the oxyanion hole connected by a water molecule. This triad has a natural attraction to Endocannabinoids, specifically 2-arachidonylglycerol (2-AG). 2-AG contributes to brain signals (neurons) to suppress the pain pathways when a patient is feeling depressed or suffering from any type of pain.

Catalytic Triad of MGL structure

Binding

2-AG binds to the catalytic triad and is hydrolyzed. The structure of 2-AG contains a long and flexible aliphatic chain and a polar head that is cleaved. 2-AG is broken down into arachidonic acid and glycerol which makes 2-AG inactive. See Overall Reaction.

Inhibition

Research on MGL is being geared towards inhibiting 2-AG from binding to the catalytic triad and being hydrolyzed. The binding of 2-AG to the catalytic triad can not be inhibited, but it can be extracted before being hydrolyzed. MPD (2-methyl-pentane-2,4-diol)is located at the end of the tunnel where the catalytic triad is at and the tunnel is filled with MPD molecules. MPD being in the same vicinity will extract 2-AG from the triad and the MPD molecule will sit in there in place of 2-AG. This natural inhibition phenomenon is known as interfacial activation.

Ligand Binding Site

Ligand within the Overall Structure of MGL

Overall Reaction

In this reaction 2-AG binds to the catalytic triad in the oxyanion hole in the active site. In the oxyanion hole the oxygen of the substrate is stabilized by two nitrogen atoms during the transition step of the catalytic reaction. The triad activates the nucleophilic serine and cleaves the ester bond of 2-AG that is being stabilized by its carbonyl group that is attached to the oxyanion hole. The glycerol molecule is released and it might diffuse to the narrow "exit hole", while the arachidonic acid would diffuse back to the top of the tunnel and leave the protein.

Literature

Additional Resources

Serine hydrolases

References

External links