Molecular characterization of a novel beta1,3-galactosyltransferase for capsular polysaccharide synthesis by Streptococcus agalactiae type Ib.
A group B streptococcus, Streptococcus agalactiae type Ib, produces a high-molecular-weight polysaccharide consisting of the following pentasaccharide repeating unit: -->4)-[alpha-D-NeupNAc-(2-->3)-beta-D-Galp-(1-->3)-beta-D-GlcpNAc-(1-->3)]-beta-D-Galp-(1-->4)-beta-D-Glcp-(1-->. The type-specific capsular polysaccharide (CP) synthesis (cps) genes of this strain were cloned and analyzed. A cloned 10-kb DNA fragment contained cpsIbE to L and neu (neuraminic acid synthesis gene) B. Comparison of the gene products with those of S. agalactiae type Ia, which has a similar but distinct CP, showed that the translation products of cpsIa and cpsIb genes exhibited very high homology except for those of cpsJ and K. In the type Ia strain, cpsIaJ encodes beta1,4-galactosyltransferase, which catalyzes the transfer of galactose as the fourth monosaccharide of the sugar repeating unit. In the type Ib CP, this galactose forms a beta1,3-linkage to GlcNAc. The low homology between the type Ia and Ib CpsJs seems to reflect this difference. By enzymatic activity measurement, the cpsIbJ product was found to display beta1,3-galactosyltransferase activity. Furthermore, hydrophobic cluster analysis clarified the similarities and differences of the structures in N-terminal regions, including the DXD motif, between the galactosyltransferases.
Watanabe
Masaki
M
Department of Biotechnology, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan.
Miyake
Katsuhide
K
Yanae
Kouji
K
Kataoka
Yohei
Y
Koizumi
Satoshi
S
Endo
Tetsuo
T
Ozaki
Akio
A
Iijima
Shinji
S
D000595:Amino Acid Sequence; D016667:Bacterial Capsules / Q000096:biosynthesis / Q000235:genetics*; D002240:Carbohydrate Sequence; D003001:Cloning, Molecular; D004269:DNA, Bacterial; D004926:Escherichia coli; D005700:Galactosyltransferases / Q000235:genetics* / Q000378:metabolism; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D010957:Plasmids; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D013292:Streptococcus agalactiae / Q000235:genetics*; D014158:Transcription, Genetic
D004269:DNA, Bacterial; D005700:Galactosyltransferases