Structure of the α-1,6/α-1,4-specific glucansucrase GTFA from lactobacillus reuteri 121

Abstract

The reuteransucrase GTFA from Lactobacillus reuteri 121, which belongs to glycosyl hydrolase family GH70, synthesizes branched -glucans with both - 1,6- and -1,4-glycosidic linkages (reuteran) from sucrose. The crystal structure of GTFA-N, a 118 kDa fragment of GTFA comprising residues 745-1763 and including the catalytic domain, was determined at 3.6 A resolution by molecular replacement. The crystals have large solvent channels and an unusually high solvent content of 85%. GTFA-N has the same domain arrangement and domain topologies as observed in previously determined GH70 glucansucrase structures. The architecture of the GTFA-N active site and binding pocket confirms that glucansucrases have a conserved substrate specificity for sucrose. However, this first crystal structure of an -1,6/-1,4-specific glucansucrase shows that residues from conserved sequence motif IV (1128-1136 in GTFA-N) contribute to the acceptor-binding subsites and that they display differences compared with other structurally characterized glucansucrases. In particular, the structure clarifies the importance of residues following the transition-state stabilizer for product specificity, and especially residue Asn1134, which is in a position to interact with sugar units in acceptor subsite +2. © 2012. © 2012 International Union of Crystallography All rights reserved.