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Applied and Environmental Microbiology, May 2000, p. 1923-1927, Vol. 66, No. 5
Department of Oral Biology, The Dental
School, University of Newcastle upon Tyne, Newcastle upon Tyne,
United Kingdom,1 and Centre de Recherche
sur les Macromolécules Végétales, CERMAV-CNRS,
affiliated with the Joseph Fourier University of Grenoble, 38041 Grenoble Cedex 9, France2
Received 19 November 1999/Accepted 2 February 2000
Glucansucrases of oral streptococci and Leuconostoc
mesenteroides are enzymes of medical and biotechnological
interest that synthesize
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Mutagenesis of Asp-569 of Glucosyltransferase I
Glucansucrase Modulates Glucan and Oligosaccharide Synthesis
-glucans. They can also synthesize
oligosaccharides in the presence of a sugar acceptor. Previous reports
have identified an amino acid residue that may affect the structure of
the glucan product; therefore, random mutagenesis of the corresponding
Asp-569 of Streptococcus downei glucosyltransferase I
(GTF-I) was used to further understanding of its involvement in the
catalytic mechanism and to evaluate how different amino acids can
modulate glucan and oligosaccharide synthesis. GTF-I variants were
obtained where Asp-569 was replaced by each of the different possible
classes of amino acids. These were expressed in Escherichia
coli and purified by means of a His6 tag. The results
showed that the amino acid in position 569 influences the structure of
the glucan and the size of the oligosaccharides produced by GTF-I. The
results suggest that the amino acid occupying this position is more
likely to interact with the acceptor molecules (oligosaccharides or
elongating glucan chain) than to be directly involved in glucosyl
transfer from sucrose. Engineering of the equivalent position in
glucansucrases thus appears to be a good target to expand the range of
oligosaccharides synthesized.
*
Corresponding author. Mailing address: Department of
Oral Biology, Dental School, University of Newcastle upon Tyne,
Newcastle upon Tyne NE2 4BW, United Kingdom. Phone: 44 191 222 7859. Fax: 44 191 222 6137. E-mail:
r.r.russell{at}newcastle.ac.uk.
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