Ax. Li et Jc. Steffens, An acyltransferase catalyzing the formation of diacylglucose is a serine carboxypeptidase-like protein, P NAS US, 97(12), 2000, pp. 6902-6907
Citations number
46
Categorie Soggetti
Multidisciplinary
Journal title
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
1-O-beta-acyl acetals serve as activated donors in group transfer reactions
involved in plant natural product biosynthesis and hormone metabolism. How
ever, the acyltransferases that mediate transacylation from 1-O-beta-acyl a
cetals have not been identified. We report the identification of a cDNA enc
oding a 1-O-beta-acylglucose-dependent acyltransferase functioning in gluco
se polyester biosynthesis by Lycopersicon pennellii, The acyltransferase cD
NA encodes a serine carboxypeptidase-like protein, with a conserved Ser-His
-Asp catalytic triad, Expression of the acyltransferase cDNA in Saccharomyc
es cerevisiae conferred the ability to disproportionate 1-O-beta-acylglucos
e to diacylglucose. The disproportionation reaction is regiospecific, catal
yzing the conversion of two equivalents of 1-O-beta-acylglucose to 1,2-di-O
-acylglucose and glucose, Diisopropyl fluorophosphate, a transition-state a
nalog inhibitor of serine carboxypeptidases, inhibited acyltransferase acti
vity and covalently labeled the purified acyltransferase, suggesting the in
volvement of an active serine in the mechanism of the transacylation, The a
cyltransferase exhibits no carboxypeptidase activity; conversely, the serin
e carboxypeptidases we have tested show no ability to transacylate using 1-
O-acyl-beta-glucoses. This acyltransferase may represent one member of a br
oader class of enzymes recruited from proteases that have adapted a common
catalytic mechanism of catabolism and modified it to accommodate a wide ran
ge of group transfer reactions used in biosynthetic reactions of secondary
metabolism. The abundance of serine carboxypeptidase-like proteins in plant
s suggests that this motif has been used widely for metabolic functions.