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2b39

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Revision as of 13:57, 20 March 2008 by OCA (Talk | contribs)
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Image:2b39.gif


PDB ID 2b39

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, resolution 3.0Å
Coordinates: save as pdb, mmCIF, xml



Structure of mammalian C3 with an intact thioester at 3A resolution


Overview

The third component of complement (C3) is a 190 kDa glycoprotein essential for eliciting the complement response. The protein consists of two polypeptide chains (alpha and beta) held together with a single disulfide bridge. The beta-chain is composed of six MG domains, one of which is shared with the alpha-chain. The disulfide bridge connecting the chains is positioned in the shared MG domain. The alpha-chain consists of the anaphylatoxin domain, three MG domains, a CUB domain, an alpha(6)/alpha(6)-barrel domain and the C-terminal C345c domain. An internal thioester in the alpha-chain of C3 (present in C4 but not in C5) is cleaved during complement activation. This mediates covalent attachment of the activated C3b to immune complexes and invading microorganisms, thereby opsonizing the target. We present the structure of bovine C3 determined at 3 Angstroms resolution. The structure shows that the ester is buried deeply between the thioester domain and the properdin binding domain, in agreement with the human structure. This domain interface is broken upon activation, allowing nucleophile access. The structure of bovine C3 clearly demonstrates that the main chain around the thioester undergoes a helical transition upon activation. This rearrangement is proposed to be the basis for the high level of reactivity of the thioester group. A strictly conserved glutamate residue is suggested to function catalytically in thioester proteins. Structure-based design of inhibitors of C3 activation may target a conserved pocket between the alpha-chain and the beta-chain of C3, which appears essential for conformational changes in C3.

About this Structure

2B39 is a Single protein structure of sequence from Bos taurus. Full crystallographic information is available from OCA.

Reference

The structure of bovine complement component 3 reveals the basis for thioester function., Fredslund F, Jenner L, Husted LB, Nyborg J, Andersen GR, Sottrup-Jensen L, J Mol Biol. 2006 Aug 4;361(1):115-27. Epub 2006 Jun 21. PMID:16831446

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