 There are also sMAP (also called MAp19) and MAp44, which do not have protease domains and are thought to be regulatory molecules of MASPs.MASPs also form complexes with ficolins, which are similar to MBL functionally and structurally with the exception that ficolins recognize their targets through fibrinogen-like domains, unlike MBL.In order to activate the complement system when MBL binds to its target (for example, mannose on the surface of a bacterium), the MASP protein functions to cleave the blood protein C4 into C4a and C4b.