Complement C1QB

Human complement C1q subcomponent subunit B (C1QB) is a 25 kDa polypeptide chain with 253 amino acids. Similar to C1QA, C1QB consists of a collagen-like ‘stalk’ at the N terminus and a globular ‘head’ at the C terminal. Human complement C1q is a protein complex composed of six heterotrimers, each of which contains a C1QA, a C1QB, and a C1QC chain. Each heterotrimer is noncovalently linked to each other, and in the heterotrimer, there are three polypeptide chains are connected by disulfide bonds. Thus, the C-terminal portion of these chains in each heterotrimer form the globular ‘head’ of complement C1q (gC1q), and the N- terminal sequences form the collagen-like region of complement C1q (cC1q).

As a critical component of complement C1q, C1QB expression is directly related to the function of C1q and complement classical pathway activation. Diseases associated with C1QB abnormity mainly include C1q deficiency, autoimmune diseases, immunodeficiency, and Alzheimer’s disease.

Fig. 1 Structure and assembly of C1QB subunit.¹

Reference

1. Ain, Danyaal, et al. "The role of complement in the tumor microenvironment." Faculty Reviews 10 (2021).