C1qa, Complement C1q subcomponent subunit A, Complement component 1 q subcomponent A chain, Complement component 1 q subcomponent alpha polypeptide,
C1q associates with the proenzymes C1r and C1s to yield C1, the first component of the serum complement system. The collagen-like regions of C1q interact with the Ca(2+)-dependent C1r(2)C1s(2) proenzyme complex, and efficient activation of C1 takes place