Transglucosylation potential of six sucrose phosphorylases toward different classes of acceptors

In this study, the transglucosylation potential of six sucrose phosphorylase (SP) enzymes has been compared using eighty putative acceptors from different structural classes. To increase the solubility of hydrophobic acceptors, the addition of various co-solvents was first evaluated. All enzymes were found to retain at least 50% of their activity in 25% dimethylsulfoxide, with the enzymes from Bifidobacterium adolescentis and Streptococcus mutans being the most stable. Screening of the enzymes' specificity then revealed that the vast majority of acceptors are transglucosylated very slowly by SP, at a rate that is comparable to the contaminating hydrolytic reaction. The enzyme from S. mutans displayed the narrowest acceptor specificity and the one from Leuconostoc mesenteroides NRRL B1355 the broadest. However, high activity could only be detected on l-sorbose and l-arabinose, besides the native acceptors d-fructose and phosphate. Improving the affinity for alternative acceptors by means of enzyme engineering will, therefore, be a major challenge for the commercial exploitation of the transglucosylation potential of sucrose phosphorylase.