Acceptor Specificity of 4-α-Glucanotransferase ofThermotoga Maritima

Abstract

High-level expression of recombinant 4-α-glucanotransferase (GTase) of the hyperthermophilic bacterium Thermotoga maritima under control of the tac promoter was achieved in Escherichia coli. Various sugars and sugar derivatives were tested for their ability to act as acceptors in glucanosyl transfer by GTase. It is postulated that transfer of glucanosyl segments by GTase occurs exclusively to the C-4 hydroxyl position of a glucose moiety which itself must be linked via a glycosidic bond to another saccharide or aglycone moiety. The anomeric configuration of this glycosidic linkage seems to be important for efficient acceptor binding since the α-glucosides which participated in GTase-mediated transfer reactions were generally much better acceptors than the corresponding β-glucosides. Based on the acceptor specificity of GTase it is postulated that the acceptor part of the active site of this enzyme contains at least two binding subsites.