Processing, Assembly and Localization of a Bacillus anthracis Spore Protein
ARMY MEDICAL RESEARCH INST OF INFECTIOUS DISEASES FORT DETRICK MD
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All Bacillus spores are encased in macromolecular shells. One of these is a proteinacious shell called the coat that, in Bacillus subtilis, provides essential protective functions. In Bacillus anthracis, the spore is the infectious particle for disease. Therefore, the coat is of particular interest because it may provide essential protective functions required for the appearance of anthrax. In our study, we identified a protein component of the spore outer layers that was previously designated as BxpA. By SDS-PAGE, BxpA migrates as a 9-kD species in Sterne strains spores, and as 11- and 14-kD species in Ames strain spores, even though it has predicted masses of 35 kD and 38 kD, respectively. We investigated the possibility that BxpA is subject to post translational processing. In B. subtilis, a subset of coat proteins is proteolyzed or crosslinked by the spore proteins YabG or Tgl, respectively. To investigate the possibility that similar processing occurs in B. anthracis, we generated mutations in the yabG or tgl genes in the Sterne and Ames strains, and analyzed the effects on BxpA migration by SDS-PAGE. As expected from the functions of YabG and Tgl in B. subtilis, we found that in yabG or tgl mutants of B. anthracis, the apparent mass of BxpA increased. These data reveal a previously unobserved event in spore protein maturation in B. anthracis. We speculate that proteolysis and crosslinking are ubiquitous events in Bacillus spore assembly.
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