Affiliation:
1. Department of Preventive Dentistry, Faculty of Dental Science, Kyushu University, Fukuoka 812-8582
2. Department of Oral Health Sciences, School of Dentistry, Nihon University, Tokyo 101-8310, Japan
Abstract
ABSTRACT
Six genes (
rgpA
through
rgpF
) that were involved in assembling the rhamnose-glucose polysaccharide (RGP) in
Streptococcus mutans
were previously identified (Y. Yamashita, Y. Tsukioka, K. Tomihisa, Y. Nakano, and T. Koga, J. Bacteriol.
180:
5803-5807, 1998). The group-specific antigens of Lancefield group A, C, and E streptococci and the polysaccharide antigen of
Streptococcus sobrinus
have the same rhamnan backbone as the RGP of
S. mutans. Escherichia coli
harboring plasmid pRGP1 containing all six
rgp
genes did not synthesize complete RGP. However,
E. coli
carrying a plasmid with all of the
rgp
genes except for
rgpE
synthesized the rhamnan backbone of RGP without glucose side chains, suggesting that in addition to
rgpE
, another gene is required for glucose side-chain formation. Synthesis of the rhamnan backbone in
E. coli
required the initiation of transfer of
N
-acetylglucosamine to a lipid carrier and the expression of the
rgpC
and
rgpD
genes encoding the putative ABC transporter specific for RGP. The similarities in RGP synthesis between
E. coli
and
S. mutans
suggest common pathways for rhamnan synthesis. Therefore, we evaluated the rhamnosyl polymerization process in
E. coli
by high-resolution sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the lipooligosaccharide (LOS). An
E. coli
transformant harboring
rgpA
produced the LOS modified by the addition of a single rhamnose residue. Furthermore, the
rgpA
,
rgpB
, and
rgpF
genes of pRGP1 were independently mutated by an internal deletion, and the LOS chemotypes of their transformants were examined. The transformant with an
rgpA
deletion showed the same LOS profile as
E. coli
without a plasmid. The transformant with an
rgpB
deletion showed the same LOS profile as
E. coli
harboring
rgpA
alone. The transformant with an
rgpF
deletion showed the LOS band with the most retarded migration. On the basis of these results, we speculated that RgpA, RgpB, and RgpF, in that order, function in rhamnan polymerization.
Publisher
American Society for Microbiology
Subject
Infectious Diseases,Immunology,Microbiology,Parasitology
Cited by
58 articles.
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