Transglycosylation by Streptococcus mutans GS-5 glucosyltransferase-D: acceptor specificity and engineering of...

The acceptor specificity of Streptococcus mutans GS-5 glucosyltransferase-D (GTF-D) was studied, particular the specificity toward non-saccharide compounds. Dihydroxy aromatic compounds like catechol, 4-methylcatechol, and 3-methoxycatechol were glycosylated by GTF-D with a high efficiency. Transglycosylation yields were 65%, 50%, and 75%, respectively, using 40 mM acceptor and 200 mM sucrose as glucosyl donor. 3-Methoxylcatchol was also glycosylated, though at a significantly lower rate. A number of other aromatic compounds such as phenol, 2-hydroxybenzaldehyde, 1,3-dihydroxybenzene, and 1, 2-phenylethanediol were not glycosylated by GTF-D. Consequently GTF-D aromatic acceptors appear to require two adjacent aromatic hydroxyl groups. In order to facilitate the transglycosylation of less water-soluble acceptors the use of various water miscible organic solvents (cosolvents) was studied. The flavonoid catechin was used as a model acceptor. Bis-2-methoxyethyl ether (MEE) was selected as a useful cosolvent. In the presence of 15% (v/v) MEE the specific catechin transglucosylation activity was increased 4-fold due to a 12-fold increase in catechin solubility. MEE (10-30% v/v) could also be used to allow the transglycosylation of catechol, 4-methylcatechol, and 3-methoxycatechol at concentrations (200 mM) otherwise inhibiting GTF-D transglycosylation activity.