CapE, a 47-Amino-Acid Peptide, Is Necessary for Bacillus anthracis Polyglutamate Capsule Synthesis

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Abstract
Polyglutamate is found in various bacteria, but displays different functions depending on the species and their environment. Here, we describe a minimal polyglutamate synthesis system in Bacillus anthracis . In addition to the three genes previously described as sufficient for polyglutamate synthesis, this system includes a small open reading frame, capE , belonging to the cap operon. The polyglutamate system's requirement for the five cap genes, for capsulation and anchoring, was assayed in nonpolar mutants. The capA , capB , capC , and capE genes are all necessary and are sufficient for polyglutamate synthesis by B. anthracis. capD is required for polyglutamate anchoring to the peptidoglycan. The 47-amino-acid peptide encoded by capE is localized in the B. anthracis membrane. It is not a regulator and it is required for polyglutamate synthesis, suggesting that it has a structural role in polyglutamate synthesis. CapE appears to interact with CapA. Bacillus subtilis ywtC is similar to capE and we named it pgsE . Genes similar to capE or pgsE were found in B. subtilis natto, Bacillus licheniformis , and Staphylococcus epidermidis , species that produce polyglutamate. All the bacterial polyglutamate synthesis systems analyzed show a similar genetic organization and, we suggest, the same protein requirements.

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