This is the C-terminal domain of BclA (Bacillus collagen-like protein of anthracis) which is expressed on spores of Bacillus species. Trimers of the C-terminal domain (CTD) form the tips of the spore's hair-like nap and are the immunodominant target of vertebrate antibodies and drive trimerization [1]. Structure analysis indicate the C-terminal region of the peptide folding into an all-beta structure with a jelly-fold topology, similar to the first human complement C1q, a member of the tumor necrosis factor (TNF)-like family. The C-terminal globular domain has been shown to be located on the exterior of the exosporium, and therefore is critical in determining the immunogenicity of the spore in a mammalian host [2].

1: Variable lymphocyte receptor recognition of the immunodominant glycoprotein of Bacillus anthracis spores. Kirchdoerfer RN, Herrin BR, Han BW, Turnbough CL Jr, Cooper MD, Wilson IA; Structure. 2012;20:479-486. PMID:22405006

2: Construction, crystal structure and application of a recombinant protein that lacks the collagen-like region of BclA from Bacillus anthracis spores. Liu CQ, Nuttall SD, Tran H, Wilkins M, Streltsov VA, Alderton MR; Biotechnol Bioeng. 2008;99:774-782. PMID:17879302