Complement Component C1q

**Semantic type:** Amino Acid, Peptide, or Protein

**Definition:** A protein complex composed of 18 complement component 1q (C1q) subcomponent chains: six C1qA, six C1qB and six C1qC. The C1q complex is part of the complement component C1 complex (C1 complex) and undergoes confirmational rearrangement following binding of pentraxins or antigen-antibody complexes that include either immunoglobulin M (IgM) or several IgG molecules. These confirmational changes activate the C1r chains of the C1 complex, which, in turn, cleaves C1s chains of the C1 complex. Following C1s cleavage, the C1 complex can proteolytically activate C2 and C4 and promotes formation of C3-convertase, which cleaves C3 and activates the classical complement pathway.

**Synonyms:** - C1q - C1q Complex - COMPLEMENT C1Q - Complement C1q - Complement Component C1q Complex