2i6q

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Template:STRUCTURE 2i6q

Complement component C2a

Overview

C2a provides the catalytic center to the convertase complexes of the classical and lectin-binding pathways of complement activation. We determined two crystal structures of full-length C2a, with and without a pseudo ligand bound. Both structures reveal a near-active conformation of the catalytic center of the serine protease domains, while the von Willebrand factor A-type domains display an intermediate activation state of helix alpha7 with an open, activated metal-ion-dependent adhesion site. The open adhesion site likely serves to enhance the affinity for the ligand C4b, similar to "inside-out" signaling in integrins. Surprisingly, the N-terminal residues of C2a are buried in a crevice near helix alpha7, indicative of a structural switch between C2 and C2a. Extended loops on the protease domain possibly envelop the protruding anaphylatoxin domain of the substrate C3. Together with a putative substrate-induced completion of the oxyanion hole, this may contribute to the high substrate specificity of the convertases.

About this Structure

2I6Q is a Single protein structure of sequence from Homo sapiens. Full crystallographic information is available from OCA.

Reference

Structure of complement component C2A: implications for convertase formation and substrate binding., Milder FJ, Raaijmakers HC, Vandeputte MD, Schouten A, Huizinga EG, Romijn RA, Hemrika W, Roos A, Daha MR, Gros P, Structure. 2006 Oct;14(10):1587-97. PMID:17027507 Page seeded by OCA on Sun May 4 07:08:41 2008