Elucidation of the substrate specificity of the MASP-2 protease of the lectin complement pathway and identification of the enzyme as a major physiological target of the serpin, C1-inhibitor.
Complement is a central component of host defence, but unregulated activation can contribute to disease. The system can be initiated by three pathways: classical, alternative and lectin. The classical and lectin pathways are initiated by the C1 and mannose-binding lectin (MBL) or ficolin complexes, respectively, with C1s the executioner protease of the C1 complex and MASP-2 its counterpart in the lectin complexes. These proteases in turn cleave the C4 and C2 components of the system. Here we have elucidated the cleavage specificity of MASP-2 using a randomised substrate phage display library. Apart from the crucial P1 position, the MASP-2 S2 and S3 subsites (in that order) play the greatest role in determining specificity, with Gly residues preferred at P2 and Leu or hydrophobic residues at P3. Cleavage of peptide substrates representing the known physiological cleavage sequences in C2, C4 or the serpin C1-inhibitor (a likely regulator of MASP-2) revealed that MASP-2 is up to 1000 times more catalytically active than C1s. C1-inhibitor inhibited MASP-2 50-fold faster than C1s and much faster than any other protease tested to date, implying that MASP-2 is a major physiological target of C1-inhibitor.
Kerr
Felicity K
FK
Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria 3800, Australia.
Thomas
Adele R
AR
Wijeyewickrema
Lakshmi C
LC
Whisstock
James C
JC
Boyd
Sarah E
SE
Kaiserman
Dion
D
Matthews
Antony Y
AY
Bird
Phillip I
PI
Thielens
Nicole M
NM
Rossi
Véronique
V
Pike
Robert N
RN
D003172:Complement C1 / Q000737:chemistry / Q000235:genetics / Q000276:immunology; D050718:Complement C1 Inhibitor Protein / Q000737:chemistry* / Q000235:genetics / Q000276:immunology; D003175:Complement C2 / Q000737:chemistry / Q000235:genetics / Q000276:immunology; D003181:Complement C4 / Q000737:chemistry / Q000235:genetics / Q000276:immunology; D037582:Complement Pathway, Mannose-Binding Lectin / Q000502:physiology*; D006801:Humans; D037601:Mannose-Binding Lectin / Q000737:chemistry / Q000235:genetics / Q000276:immunology; D050606:Mannose-Binding Protein-Associated Serine Proteases / Q000737:chemistry* / Q000235:genetics / Q000276:immunology; D019151:Peptide Library; D013379:Substrate Specificity / Q000502:physiology
D003172:Complement C1; D050718:Complement C1 Inhibitor Protein; D003175:Complement C2; D003181:Complement C4; D037601:Mannose-Binding Lectin; D019151:Peptide Library; C105296:MASP2 protein, human; D050606:Mannose-Binding Protein-Associated Serine Proteases