Identification of a novel gene, dep, associated with depolymerization of the capsular polymer in Bacillus anthracis

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Abstract
Bacillus anthracis produces a gamma‐linked poly‐D‐glutamic acid capsule that is essential for virulence. A 6.2 kb fragment of B. anthracis DNA (cap), when present in Escherichia coli, produces a capsular polymer that is immunologically identical to that produced by B. anthracis. By immunodiffusion analysis of E. coli strains carrying varying portions of the cap region, we identified a novel gene (dep) responsible for degradation of the capsular polymer of B. anthracis. The simultaneous presence of the cap region and the dep gene caused production of low‐molecular‐weight, degraded capsular polymer both in E. coli and in B. anthracis, whereas the cap region atone caused production of a high‐molecular‐weight capsule. The dep gene mapped immediately downstream of the cap region within a 1.8 kb fragment and was transcribed in the same direction. This fragment was sequenced and a 1401 bp open reading frame (ORF) was found that is predicted to encode a peptide with molecular weight of 51460. By in vitro transcription‐translation analysis, this ORF was shown to be the dep gene product. The deduced amino acid sequence of the dep product has sequence similarity to E. coli and mammalian γ‐glutamyltranspeptidase (GGT). However, the Dep protein did not have GGT activity. The Dep protein appears to be an enzyme that catalyses the hydrolysis of the poly‐D‐glutamic acid capsule. Although the biological functions of the dep gene are unknown, it is possible that low‐molecular‐weight, diffusible polyglutamates produced through the action of the dep gene may act to inhibit host defence mechanisms.