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A critical cysteine residue in monoacylglycerol lipase is targeted by a new class of isothiazolinone-based enzyme inhibitors

  • Author(s): King, AR
  • Lodola, A
  • Carmi, C
  • Fu, J
  • Mor, M
  • Piomelli, D
  • et al.
Abstract

Background and purpose: Monoacylglycerol lipase (MGL) is a presynaptic serine hydrolase that inactivates the endocannabinoid neurotransmitter, 2-arachidonoyl-sn-glycerol. Recent studies suggest that cysteine residues proximal to the enzyme active site are important for MGL function. In the present study, we characterize the role of cysteines in MGL function and identify a series of cysteine-reactive agents that inhibit MGL activity with nanomolar potencies by interacting with cysteine residue 208. Experimental approach: A series of cysteine traps were screened for the ability to inhibit MGL in vitro. Rapid dilution assays were performed to determine reversibility of inhibition. Molecular modelling and site-directed mutagenesis were utilized to identify cysteine residues targeted by the inhibitors. Key results: The screening revealed that 2-octyl-4-isothiazolin-3-one (octhilinone) inhibited purified rat recombinant MGL (IC50 = 88 12 nM) through a partially reversible mechanism. Initial structure-activity relationship studies showed that substitution of the n-octyl group of octhilinone with a more lipophilic oleoyl group increased inhibitor potency (IC50 = 43 8 nM), while substitution with a methyl group produced the opposite effect (IC50 = 239 68 nM). The inhibitory potency of octhilinone was selectively decreased by mutating cysteine 208 in MGL to glycine (IC50; wild-type, 151 17 nM; C208G, 722 74 nM), but not by mutation of other cysteine residues (C32, C55, C201, C208 and C242).Conclusions and mplications: The results indicated that cysteine 208 plays an important role in MGL function and identified a novel class of isothiazolinone-based MGL inhibitors with nanomolar potency in vitro. © 2009 The British Pharmacological Society All rights reserved.

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