MASP

(= MBL-associated serine protease)

Proteases (ca 76 kD) in the complement system, activated by the binding of mannan to mannan-binding lectin (MBL), (formerly mannose-binding protein, MBP). MASP-1 and MASP-2 are similar to the C1q-associated proteases, C1r and C1s. All four have a C1r/C1s-like domain, an EGF-like domain and a second C1r/C1s-like domain, two complement control protein (CCP) domains and a serine protease domain. MASP-1 and MASP-2 are probably responsible for the proteolytic cleavage and activation of C2 and C4.