Four glucosyltransferases, GtfJ, GtfK, GtfL and GtfM, from Streptococcus salivarius ATCC 25975.

The four recombinant glucosyltransferases (GTFs), GtfJ, GtfK, GtfL and GtfM, that had previously been cloned from Streptococcus salivarius ATCC 25975, were individually expressed in Escherichia coli and their glucan products and kinetic properties were analysed. GtfJ was a primer-dependent GTF which synthesized an insoluble glucan composed mainly of alpha-(1-->3)-linked glucosyl residues in the presence of dextran T-10. GtfK was primer-stimulated, and produced a linear soluble dextran without any detectable branch points both in the absence and in the presence of dextran T-10. GtfL was primer-independent and produced a mixed-linkage insoluble glucan composed of approximately equal proportions of alpha-(1-->3)- and alpha-(1-->6)-linked glucosyl residues. GtfL was inhibited by dextran T-10. GtfM was primer-independent and produced a soluble dextran with approximately 5% alpha-(1-->3)-linked glucosyl residues. GtfM was essentially unaffected by the presence of dextran T-10. The results confirmed that each enzyme represented one of the four possible combinations of primer-dependency and product solubility and that each possessed unique biosynthetic properties. The soluble dextrans formed by GtfK and GtfM, as well as the mixed-linkage insoluble glucan formed by GtfL, were also capable of acting as primers for the primer-dependent GtfJ and the primer-stimulated GtfK. Unexpectedly, the linear dextran produced by GtfK was by far the least effective either at priming itself or at activating and priming the primer-dependent GtfJ.