Mannose-binding lectin serine proteases and associated proteins of the lectin pathway of complement: two genes, five proteins and many functions?

Biochim Biophys Acta. 2012 Jan;1824(1):253-62. doi: 10.1016/j.bbapap.2011.05.021. Epub 2011 Jun 6.


The lectin pathway of the complement system is activated following the binding of carbohydrate-based ligands by recognition molecules such as mannose-binding lectin (MBL) or ficolins. Engagement of the recognition molecules causes activation of associated MBL-associated serine proteases or MASPs, which in turn activate downstream complement molecules to activate the system. Two MASP genes are alternatively spliced during expression to yield 5 proteins, including three proteases (MASP-1, -2 and -3) and two truncated proteins, MAp19 and MAp44. Here we discuss what is currently known about these proteins in terms of their structure and function. MASP-2 is autoactivated following the initial binding events of the pathway and is able to subsequently activate the C4 and C2 substrates required to activate the rest of the pathway. MASP-1 is able to augment MASP-2 activation, but also appears to play other roles, although the physiological significance of these is not yet clear. The roles of the truncated Map19 and Map44 proteins and the MASP-3 protease are currently unknown. The proteases form an interesting sub-family of proteins that clearly should be the focus of future research in order to establish their biological roles. This article is part of a Special Issue entitled: Proteolysis 50 years after the discovery of lysosome.

Publication types

  • Research Support, Non-U.S. Gov't
  • Review

MeSH terms

  • Animals
  • Carrier Proteins / genetics
  • Carrier Proteins / metabolism
  • Carrier Proteins / physiology*
  • Complement Activation / genetics
  • Complement System Proteins / genetics
  • Complement System Proteins / metabolism*
  • Genes / physiology
  • Humans
  • Lectins / chemistry
  • Lectins / genetics
  • Lectins / metabolism*
  • Mannose-Binding Protein-Associated Serine Proteases / chemistry
  • Mannose-Binding Protein-Associated Serine Proteases / genetics
  • Mannose-Binding Protein-Associated Serine Proteases / metabolism*
  • Models, Biological
  • Models, Molecular
  • Signal Transduction / genetics
  • Signal Transduction / physiology
  • Structure-Activity Relationship


  • Carrier Proteins
  • Lectins
  • Complement System Proteins
  • Mannose-Binding Protein-Associated Serine Proteases