Cleavage of beta-lactone ring by serine protease. Mechanistic implications.
Both enantiomers of 3-benzyl-2-oxetanone (1) were found to be slowly hydrolyzed substrates of alpha-chymotrypsin having k(cat) values of 0.134+/-0.008 and 0.105+/-0.004 min(-1) for (R)-1 and (S)-1, respectively, revealing that alpha-CT is virtually unable to differentiate the enantiomers in the hydrolysis of 1. The initial step to form the acyl-enzyme intermediate by the attack of Ser-195 hydroxyl on the beta-lactone ring at the 2-position in the hydrolysis reaction may not be enzymatically driven, but the relief of high ring strain energy of beta-lactone may constitute a major driving force. The deacylation step is also attenuated, which is possibly due to the hydrogen bond that would be formed between the imidazole nitrogen of His-57 and the hydroxyl group generated during the acylation in the case of (R)-1, but in the alpha-CT catalyzed hydrolysis of (S)-1 the imidazole nitrogen may form a hydrogen bond with the ester carbonyl oxygen.
Kim
Dong H
DH
Division of Molecular and Life Sciences, Center for Integrated Molecular Systems, Pohang University of Science and Technology, San 31 Hyojadong, Pohang, South Korea 790-784. dhkim@postech.ac.kr
Park
Jeong-il
JI
Chung
Sang J
SJ
Park
Jung Dae
JD
Park
No-Kyung
NK
Han
Jong Hoon
JH
D000818:Animals; D001665:Binding Sites; D002384:Catalysis; D002918:Chymotrypsin / Q000378:metabolism; D006801:Humans; D006868:Hydrolysis; D007700:Kinetics; D007783:Lactones / Q000378:metabolism*; D008958:Models, Molecular; D012697:Serine Endopeptidases / Q000378:metabolism*; D013237:Stereoisomerism
D007783:Lactones; D012697:Serine Endopeptidases; D002918:Chymotrypsin; C117608:alpha-chymotrypsin