C-terminal domain of Borrelia burgdorferi protein BBK32, and similar proteins
This model includes the C-terminal domain of protein BBK32, termed BBK32-C, from Borrelia burgdorferi, the Lyme disease causing spirochete. The lipoprotein BBK32 blocks the activation of the classical pathway of complement in the host by binding to and inhibiting the initiating serine protease of the human classical complement pathway, C1r. It does so via the C-terminal domain (BBK32-C), and thereby prevents both its autocatalytic and C1s cleavage activities within the C1 complex. Mutation and comparative studies with BBK32-C homologs in B. garinii (BGD19) and B. afzelii (BAD16) identified three surface-exposed residues that are important in their potential relevance in C1r binding and inhibition, thus providing new insight into complement evasion mechanisms of Lyme-associated spirochetes of B. burgdorferi. BBK32-C adopts an anti-parallel four-helix bundle fold with a fifth alpha-helix protruding from the helical core.
Comment:these three residues contribute to the unique inhibitory activity of BBK32 and BAD16, while in BGD19 these residues are different and contribute to its reduced inhibitory activity
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