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Bacillus anthracis CapD, belonging to the γ‐glutamyltranspeptidase family, is required for the covalent anchoring of capsule to peptidoglycan
Author(s) -
Candela Thomas,
Fouet Agnès
Publication year - 2005
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.2005.04718.x
Subject(s) - peptidoglycan , operon , biology , bacillus anthracis , mutant , microbiology and biotechnology , biochemistry , covalent bond , strain (injury) , bacteria , enzyme , gene , chemistry , genetics , anatomy , organic chemistry
Summary Several examples of bacterial surface‐structure anchoring have been described, but they do not include polyglutamate capsule. Bacillus anthracis capsule, which is composed only of poly‐γ‐ d ‐glutamate, is one of the two major virulence factors of the bacterium. We analysed its anchoring. We report that the polyglutamate is anchored directly to the peptidoglycan and that the bond is covalent. We constructed a capD mutant strain, capD being the fourth gene of the capsule biosynthetic operon. The mutant bacilli are surrounded by polyglutamate material that is not covalently anchored. Thus, CapD is required for the covalent anchoring of polyglutamate to the peptidoglycan. Sequence similarities suggest that CapD is a γ‐glutamyltranspeptidase. Furthermore, CapD is cleaved at the γ‐glutamyltranspeptidase consensus cleavage site, and the two subunits remain associated, as necessary for γ‐glutamyltranspeptidase activity. Other Gram‐positive γ‐glutamyltranspeptidases are secreted, but CapD is located at the Bacillus surface, associated both with the membrane and the peptidoglycan. Polyglutamate is hydrolysed by CapD indicating that it is a CapD substrate. We suggest that CapD catalyses the capsule anchoring reaction. Interestingly, the CapD – strain is far less virulent than the parental strain.