Merck, C1740-1MG, Complement component C1q from human serum

General description
C1q, together with C1r and C1s, in the ratio of 1:2:2, form the C1 complex which is the first component of the classical complement pathway. C1q is composed of 18 polypeptide chains (six A, six B, six C) (MW 460 kDa). All contain an 81-aa collagen-like region composed of (Gly-Xaa-Yaa) repeating sequences close to the N-terminus. Three chains (A₁B₁C₁) form a triple helix with the C-terminus forming the globular heads which may be structurally and functionally distinct domains.
Application
Complement component C1q is an important regulator factor for platelet activation. This has been a topic for research, as platelet-leukocyte aggregates play an important role in inflammatory conditions such as coronary heart disease. In particular, C1q has been shown to inhibit collagen induced aggregation and enhance production of reactive oxygen species (ROS).
Biochem/physiol Actions
C1q deficiency, either because of rare homozygous genetic defect, or transcriptional/translational defects, is almost certainly a cause of systemic lupus erythematosus (SLE). The three C1q subunits are expressed through a novel mechanism of transcriptional synchronization.
Physical form
Supplied as a solution in 10 mM HEPES, 300 mM NaCl, pH 7.2