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

Felicity Kate Kerr, Adele Rene Thomas, Lakshmi Carmel Wijeyewickrema, James Whisstock, Sarah Elizabeth Boyd, Dion Kaiserman, Antony Yaron Matthews, Phillip Ian Bird, Nicole M Thielens, Veronique Rossi, Robert Neil Pike

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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 P(1) position, the MASP-2 S(2) and S(3) subsites (in that order) play the greatest role in determining specificity, with Gly residues preferred at P(2) and Leu or hydrophobic residues at P(3). 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.
Original languageEnglish
Pages (from-to)670 - 677
Number of pages7
JournalMolecular Immunology
Publication statusPublished - 2008

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