Complement C1q subcomponent subunit A (C1QA)

C1q associates with the proenzymes C1r and C1s to yield C1, the first component of the serum complement system. The collagen-like areas of C1q interact with the Ca(2+)-dependent C1r(2)C1s(2) proenzyme complex, and efficient activation of C1 occurs on interaction of the globular heads of C1q with the Fc regions of IgG or IgM antibody present in immune complexes.

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