A family of molecules (L-ficolin/P35, H-ficolin/Hakata antigen, M-ficolin, ~300 aa) that, together with mannose-binding lectin (MBL), act as immune sensors and activate the lectin complement pathway. When they bind to markers on microbial surfaces they trigger the cleavage of complement C4 by the serine peptidase MASP2 (MBL-associated serine protease-2). They are structurally similar to collectins, conglutinin, and surfactant proteins A and D and have a central collagen-like triple-helical region with a C-terminal fibrinogen-like domain. L- and H-ficolin are found in serum, M-ficolin in leucocytes. Polymorphisms in the ficolin 1 gene (FCN1) are associated with susceptibility to the development of rheumatoid arthritis.
Subjects: Medicine and Health — Chemistry.