title: Mannose-binding lectin serine proteases and associated proteins of the lectin pathway of complement: two genes, five proteins and many functions?
abstract: 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.
authors.affiliation: Department of Biochemistry & Molecular Biology, Monash University, Clayton, Victoria, Australia. tang.yongqing@monash.edu
authors.forename: Tang
authors.initials: T
authors.lastname: Yongqing
authors.forename: Nicole
authors.initials: N
authors.lastname: Drentin
authors.forename: Renee C
authors.initials: RC
authors.lastname: Duncan
authors.forename: Lakshmi C
authors.initials: LC
authors.lastname: Wijeyewickrema
authors.forename: Robert N
authors.initials: RN
authors.lastname: Pike
mesh_terms: D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D003167:Complement Activation / Q000235:genetics; D003165:Complement System Proteins / Q000235:genetics / Q000378:metabolism*; D005796:Genes / Q000502:physiology; D006801:Humans; D037102:Lectins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D050606:Mannose-Binding Protein-Associated Serine Proteases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008954:Models, Biological; D008958:Models, Molecular; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology; D013329:Structure-Activity Relationship
chemical_list: D002352:Carrier Proteins; D037102:Lectins; D003165:Complement System Proteins; D050606:Mannose-Binding Protein-Associated Serine Proteases