enzyme regulation:Inhibited by SERPING1 and A2M.,function:Functions in the lectin pathway of complement, which performs a key role in innate immunity by recognizing pathogens through patterns of sugar moieties and neutralizing them. The lectin pathway is triggered upon binding of mannan-binding lectin (MBL) and ficolins to sugar moieties which leads to activation of the associated proteases MASP1 and MASP2. Functions as an endopeptidase and may activate MASP2 or C2 or directly activate C3 the key component of complement reaction. Isoform 2 may have an inhibitory effect on the activation of the lectin pathway of complement or may cleave IGFBP5.,PTM:Autoproteolytic processing of the proenzyme produces the active enzyme composed on the heavy and the light chain held together by a disulfide bond. Isoform 1 but not isoform 2 is activated through autoproteolytic processing.,PTM:N-glycosylated. Some N-linked glycan are of the complex-type.,PTM:The iron and 2-oxoglutarate dependent 3-hydroxylation of aspartate and asparagine is (R) stereospecific within EGF domains.,similarity:Belongs to the peptidase S1 family.,similarity:Contains 1 EGF-like domain.,similarity:Contains 1 peptidase S1 domain.,similarity:Contains 2 CUB domains.,similarity:Contains 2 Sushi (CCP/SCR) domains.,subunit:Homodimer. Interacts with the oligomeric lectins MBL2, FCN2 and FCN3; triggers the lectin pathway of complement through activation of C3. Interacts with SERPING1.,tissue specificity:Protein of the plasma which is primarily expressed by liver.,