Biologia, Bratislava, 57/Suppl. 11: 129-136, 2002.

ISSN 0006-3088 (Biologia).


Full Paper

Glucan binding domain of streptococcal glucosyltransferases.


Deepan Shah & Roy R. B. Russell*

Oral Biology, Dental School, University of Newcastle, Newcastle upon Tyne, NE2 4BW, UK; tel.: ++ 44 191 222 7859, fax: ++ 44 191 222 6137, e-mail:

* corresponding author

Received: October 15, 2001 / Accepted: February 12, 2002



Glucosyltransferase I (GTF-I) of Streptococcus downei synthesises an insoluble a-1,3-linked glucan from sucrose. It contains a catalytic domain that is a circularly-permuted homologue of the catalytic domain of Family 13 enzymes and a C-terminal glucan-binding domain (GBD) that consists of a series of tandem repeats, each ~35 amino acids long. In order to examine the contribution of these repeats to binding, a nested series of plasmids was constructed that expressed truncated forms of GTF-I or GBD in Escherichia coli, with an N-terminal His6 tag. The tag facilitated rapid purification and also allowed development of a novel microtitre tray assay in which binding of biotin-labelled dextran to immobilised GTF-I or GBD could be quantitatively determined. The capacity to bind dextran was proportional to the number of repeats, with a minimum of four repeats necessary to demonstrate binding in this assay.


Key words: Streptococcus, glucan binding, dextran, Family 70.