Sequence motifs and proteolytic cleavage of the collagen-like glycoprotein BclA required for its attachment to the exosporium of Bacillus anthracis.
Bacillus anthracis spores are enclosed by an exosporium comprised of a basal layer and an external hair-like nap. The filaments of the nap are composed of trimers of the collagen-like glycoprotein BclA. The attachment of essentially all BclA trimers to the exosporium requires the basal layer protein BxpB, and both proteins are included in stable high-molecular-mass exosporium complexes. BclA contains a proteolytically processed 38-residue amino-terminal domain (NTD) that is essential for basal-layer attachment. In this report, we identify three NTD submotifs (SM1a, SM1b, and SM2, located within residues 21 to 33) that are important for BclA attachment and demonstrate that residue A20, the amino-terminal residue of processed BclA, is not required for attachment. We show that the shortest NTD of BclA-or of a recombinant protein-sufficient for high-level basal-layer attachment is a 10-residue motif consisting of an initiating methionine, an apparently arbitrary second residue, SM1a or SM1b, and SM2. We also demonstrate that cleavage of the BclA NTD is necessary for efficient attachment to the basal layer and that the site of cleavage is somewhat flexible, at least in certain mutant NTDs. Finally, we propose a mechanism for BclA attachment and discuss the possibility that analogous mechanisms are involved in the attachment of many different collagen-like proteins of B. anthracis and closely related Bacillus species.
Tan
Li
L
UAB Department of Microbiology, BBRB 409, 1530 3rd Ave. S, Birmingham, AL 35294-2170, USA.
Turnbough
Charles L
CL
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001408:Bacillus anthracis / Q000254:growth & development / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D011485:Protein Binding; D025941:Protein Interaction Mapping; D017384:Sequence Deletion; D013171:Spores, Bacterial / Q000254:growth & development / Q000378:metabolism*
C470593:BclA protein, Bacillus anthracis; D008562:Membrane Glycoproteins