Affiliation:
1. Department of Applied Oral Sciences
2. Department of Microbiology and Immunology, Faculty of Medicine, Dalhousie University, Halifax, Nova Scotia, Canada B3H 3J5
3. Department of Dental Clinical Sciences, Faculty of Dentistry
Abstract
ABSTRACT
Sortase is a newly discovered transpeptidase that covalently links LPXTGX-containing surface proteins to the gram-positive bacterial cell wall. In this study, the sortase gene (
srtA
) was isolated from
Streptococcus mutans
NG8 by PCR. The gene encoded a 246-amino-acid protein, including a 40-amino-acid signal peptide. The
srtA
gene was insertionally inactivated by a tetracycline resistance cassette. P1, a major surface protein adhesin previously shown to anchor to the peptidoglycan by the LPXTGX motif, was secreted into the culture medium by the
srtA
mutant. In contrast, the wild-type P1 remained cell wall associated. Complementation of the mutant with
srtA
restored the P1 surface expression phenotype. P1 produced by the mutant, but not that produced by the wild type and the
srtA
-complemented mutant, was recognized by an antibody raised against the hydrophobic domain and charged tail C terminal to the LPXTGX motif. These results suggest that the failure to anchor P1 to the cell wall is due to the lack of cleavage of P1 at the LPXTGX motif. The
srtA
mutant was markedly less hydrophobic than the wild type and the complemented mutant. The
srtA
mutant failed to aggregate in the presence of saliva or salivary agglutinin and adhered poorly to saliva- or salivary agglutinin-coated hydroxylapatite. In rats, the
srtA
mutant colonized the teeth poorly when sucrose was absent. When sucrose was present, the
srtA
mutant colonized the teeth but less effectively and induced significantly less caries (
P
< 0.05) than the wild-type strain. In conclusion, the sortase enzyme in
S. mutans
is responsible for anchoring P1 to the cell surface and plays a role in modulating the surface properties and cariogenicity of
S. mutans
.
Publisher
American Society for Microbiology
Subject
Infectious Diseases,Immunology,Microbiology,Parasitology
Cited by
104 articles.
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