Mutation of Cys242 of Human Monoacylglycerol Lipase Disrupts Balanced Hydrolysis of 1- and 2-Monoacylglycerols and Selectively Impairs Inhibitor Potency
作者:Tuomo Laitinen、Dina Navia-Paldanius、Roosa Rytilahti、Joona J. T. Marjamaa、Julie Kařízková、Teija Parkkari、Tatu Pantsar、Antti Poso、Jarmo T. Laitinen、Juha R. Savinainen
DOI:10.1124/mol.113.090795
日期:2014.3
Considerable progress has been made in recent years in developing selective, potent monoacylglycerol lipase (MAGL) inhibitors. In the investigations of measures to inhibit this enzyme, less attention has been paid to improving our understanding of its catalytic mechanisms or substrate preferences. In our study, we used site-directed mutagenesis, and we show via versatile activity assays combined with molecular modeling that Cys242 and Tyr194, the two opposing amino acid residues in the catalytic cavity of MAGL, play important roles in determining the rate and the isomer preferences of monoacylglycerol hydrolysis. In contrast to wild-type enzymes that hydrolyzed 1- and 2-monoacylglycerols at similar rates, mutation of Cys242 to alanine caused a significant reduction in overall activity (maximal velocity, V max), particularly skewing the balanced hydrolysis of isomers to favor the 2-isomer. Molecular modeling studies indicate that this was caused by structural features unfavorable toward 1-isomers as well as impaired recognition of OH-groups in the glycerol moiety. Direct functional involvement of Cys242 in the catalysis was found unlikely due to the remote distance from the catalytic serine. Unlike C242A, mutation of Tyr194 did not bias the hydrolysis of 1- and 2-monoacylglycerols but significantly compromised overall activity. Finally, mutation of Cys242 was also found to impair inhibition of MAGL, especially that by fluorophosphonate derivatives (13- to 63-fold reduction in potency). Taken together, this study provides new experimental and modeling insights into the molecular mechanisms of MAGL-catalyzed hydrolysis of the primary endocannabinoid 2-arachidonoylglycerol and related monoacylglycerols.
近年来,选择性、强效单酰基甘油酯酶(MAGL)抑制剂的研发取得了长足进展。在抑制这种酶的研究中,人们较少关注如何增进对酶催化机理或底物偏好的理解。在我们的研究中,我们采用了定点突变技术,并通过多功能活性测定与分子建模相结合的方法,证明了MAGL催化腔中两个相对的氨基酸残基Cys242和Tyr194在决定单酰基甘油酯水解速率和异构体偏好方面起着重要作用。与水解1-和2-单酰基甘油酯的速率相似的野生型酶相比,将Cys242突变为丙氨酸会导致总体活性(最大速度V max)显著降低,特别是使异构体的平衡水解偏向2-异构体。分子建模研究表明,这是由于结构特征不利于1-异构体,以及甘油部分中羟基的识别受损所致。由于与催化丝氨酸的距离较远,Cys242不太可能直接参与催化功能。与C242A不同,Tyr194突变不会影响1-和2-单酰基甘油酯的水解,但会显著降低总体活性。最后,还发现Cys242突变会削弱对MAGL的抑制作用,特别是氟磷酸酯衍生物的抑制作用(效力降低13至63倍)。总之,这项研究为MAGL催化