CapE, a 47-amino-acid peptide, is necessary for Bacillus anthracis polyglutamate capsule synthesis.

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.