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Recent progress in the understanding of the structure-function relationships of the globular head regions of C1q.

Authors
  • Kishore, Uday
  • Kojouharova, Mihaela S
  • Reid, Kenneth B M
Type
Published Article
Journal
Immunobiology
Publisher
Elsevier
Publication Date
Sep 01, 2002
Volume
205
Issue
4-5
Pages
355–364
Identifiers
PMID: 12395999
Source
Medline
License
Unknown

Abstract

The first step in the activation of the classical pathway of complement cascade by immune complexes involves the binding of the C-terminal globular head regions of C1q to the Fc regions of IgG or IgM, each globular head being composed of the C-terminal halves of one A-, one B- and one C-chain. Recent studies using recombinant forms of globular region appear to suggest that each globular head of C1q may be composed of three, structurally and functionally, independent domains/modules. The heterotrimeric organisation thus could offer functional flexibility and versatility to the whole C1q molecule. The crystal structure of an adipocyte-specific serum protein, Acrp-30, has revealed the existence of a structural fold shared by members of a new C1q/tumor necrosis factor (TNF) superfamily, characterized by a distinctive globular domain. The protein members seem to be active as self-assembling noncovalent trimers, whose individual chains fold as compact 'jellyroll' beta sandwiches. The recognition of a C1q/TNF superfamily, which has wide-ranging functions, highlights the possibility that the globular regions of C1q may fulfill more binding functions than previously envisaged.

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