Mannose Associated Serine Protease 1 (MASP1)

Mannose-associated serine protease 1 (MASP1) is involved in the lectin pathway of the complement system and is responsible for cleaving C4 and C2 to form C4b2a, a C3-convertase.Mannose-binding lectin (MBL) is a serum component which participates in innate immunity by activating complement via a novel pathway. Human MBL forms complexes with two types of serine proteases termed MASP (MBL-associated serine protease).

These two proteases, MASP1 and MASP2, are structurally similar to one another as well as to C1r and C1s. Together, MASP, C1r and C1s constitute a novel serine protease family. It is likely that human MASP1 is able to activate C3, while human MASP2 cleaves C4, although further functional studies are required to confirm this.