The mannan-binding lectin-associated serine proteases (MASPs) and MAp19: four components of the lectin pathway activation complex encoded by two genes

Immunobiology. 2002 Sep;205(4-5):455-66. doi: 10.1078/0171-2985-00146.


Mannan-binding lectin (MBL) and ficolins (L-ficolin and H-ficolin) initiate the lectin pathway of complement activation upon binding to microbial carbohydrates. The activation is mediated by associated serine proteases, termed MASPs, since they were discovered as MBL-associated serine proteases. The MASP family comprises three serine proteases, MASP-1, MASP-2 and MASP-3 and a non-enzymatic protein, MAp19. The MASPs show identical domain structure, shared also with C1r and C1s. MASP-1 and MASP-3 are alternative splice products of a single gene, MASP1/3, and have identical A chains, whereas they have individual B chains, encompassing the serine protease domain. MASP2 and MAp19 are alternative splice products of the MASP-2 gene, with MAp19 consisting of the first two domains of MASP-2 plus additional four amino acid residues. MASP-2 is the protease responsible for activating C4 and C2 to generate the C3 convertase, C4bC2b. The biological function of the remaining three proteins has not yet been resolved.

Publication types

  • Review

MeSH terms

  • Animals
  • Complement Activation / genetics
  • Complement Activation / physiology
  • Complement Pathway, Mannose-Binding Lectin / genetics*
  • Complement Pathway, Mannose-Binding Lectin / physiology
  • Humans
  • Mannose-Binding Protein-Associated Serine Proteases
  • Phylogeny
  • Serine Endopeptidases / chemistry*
  • Serine Endopeptidases / genetics*
  • Serine Endopeptidases / metabolism


  • MASP2 protein, human
  • Mannose-Binding Protein-Associated Serine Proteases
  • Serine Endopeptidases