Genes responsible for dextran-dependent aggregation of Streptococcus sobrinus strain 6715.
BACKGROUND
Streptococcus sobrinus exhibits more significant dextran-dependent aggregation mediated by glucan-binding proteins than Streptococcus mutans. We have identified four glucan-binding protein C gene (gbpC) homologues designated as gbpC1, gbpC2, dblA and dblB in S. sobrinus in contrast to the single gene gbpC in S. mutans. We attempted to determine which gene is most responsible for the dextran-dependent aggregation of S. sobrinus.


METHODS
We introduced mutation with a chemical mutagen, 1-methyl-3-nitro-1-nitrosoguanidine, into S. sobrinus strain 6715 and analysed the four gbpC homologous gene sequences in the parental strain 6715 and an obtained aggregation-negative mutant NUM-Ssg99. We also examined the localization of proteins encoded by these genes in the mutant NUM-Ssg99.


RESULTS
The nucleotide sequences of the gbpC1, gbpC2 and dblA genes in NUM-Ssg99 were 100% identical to the homologous genes in parental strain 6715. In contrast, a truncated mutation was detected in the dblB gene and the mutant protein devoid of the LPXTG motif was confirmed by Western blot analysis to be released into the extracellular milieu.


CONCLUSIONS
We conclude that the dblB gene among the four GbpC homologous protein genes is most responsible for aggregation in strain 6715.
Department of Biochemistry and Oral Health Science Center HRC7, Tokyo Dental College, Chiba City, Japan. yusato@tdc.ac.jp
Y
Y
Sato
K
K
Okamoto-Shibayama
K
K
Takada
T
T
Igarashi
M
M
Hirasawa
D020816:Amino Acid Motifs / Q000235:genetics; D019881:Aminoacyltransferases / Q000235:genetics; D001426:Bacterial Proteins / Q000235:genetics; D020029:Base Pairing / Q000235:genetics; D001483:Base Sequence / Q000235:genetics; D015153:Blotting, Western; D002352:Carrier Proteins / Q000187:drug effects / Q000235:genetics*; D002874:Chromosome Mapping; D003546:Cysteine Endopeptidases / Q000235:genetics; D003911:Dextrans; D004591:Electrophoresis, Polyacrylamide Gel; D005798:Genes, Bacterial / Q000235:genetics*; D006801:Humans; D037102:Lectins / Q000187:drug effects / Q000235:genetics*; D008769:Methylnitronitrosoguanidine; D009153:Mutagens; D009154:Mutation / Q000235:genetics; D010457:Peptidoglycan / Q000235:genetics; D010641:Phenotype; D011485:Protein Binding / Q000235:genetics; D017422:Sequence Analysis, DNA; D017384:Sequence Deletion / Q000235:genetics; D017385:Sequence Homology; D016986:Streptococcus sobrinus / Q000235:genetics* / Q000502:physiology; D000637:Transaminases / Q000235:genetics
D001426:Bacterial Proteins; D002352:Carrier Proteins; D003911:Dextrans; D037102:Lectins; D009153:Mutagens; D010457:Peptidoglycan; C037937:glucan-binding proteins; D008769:Methylnitronitrosoguanidine; D019881:Aminoacyltransferases; C120542:sortase A; D000637:Transaminases; C053430:histidinol-phosphate aminotransferase; D003546:Cysteine Endopeptidases