Synthesis of dextrans with controlled amounts of alpha-1,2 linkages using the transglucosidase GBD-CD2

GBD-CD2 is an alpha-1,2 transglucosidase engineered from DSR-E, a glucansucrase naturally produced by Leuconostoc mesenteroides NRRL B-1299. This enzyme catalyses from sucrose, the alpha-1,2 transglucosylation of glucosyl moieties onto alpha-1,6 dextran chains. Steady-state kinetic studies showed that hydrolysis and transglucosylation reactions occurred at the early stage of the reaction in the presence of 70 kDa dextran as acceptor and sucrose. The transglucosylation reaction catalysed by GBD-CD2 follows a Ping Pong Bi Bi mechanism with a high kcat value of 970 s(-1). The amount of the synthesised alpha-1,2 side chains was found to be directly dependent on the initial molar ratio [Sucrose]/[Dextran]. Dextrans with controlled alpha-1,2 linkage contents ranging from 13% to 40% were synthesised. The procedure resulted in the production of dextrans with the highest content of alpha-1,2 linkages ever reported.