Figure 1.

Schematic model of the subunit structure and assembly of intact of C1q. Three similar chains – A, B, and C – are assembled to form disulfide-linked A–B and C–C dimers. One strand of the molecule consists of an A–B dimer non-covalently linked to a C chain forming (A–B–C). The C chain of one strand is then disulfide-linked to the C chain of a neighboring strand to give an A–B C–C B–A doublet and three such doublets are linked by non-covalent forces giving C1q its final signature “bouquet-like” structure. The length of each chain as well as the length of the gC1q and cC1q domains (for brevity, g- or c-domain) is given in parenthesis. (The figure was adapted from Reid, 1989).