Fig. 1.

Schematic representation of structural organization of human C1q and of C1 assembly. A, model showing the CLR and globular heads of C1q and the association with the C1r/C1s tetramer forming the C1 complex. B, representation of the association between the A, B, and C chains leading to formation of the six ABC heterotrimeric triple helices of C1q CLR. The two following interruptions in the Gly-Y-Z triplet repeats are involved in the kink of the collagen-like region, i.e. the insertion of a threonine at position 39 in the A chain and the replacement of a glycine by an alanine at position 36 in the C chain (only the interruption in the A chain is shown).