Substrate specificities of recombinant mannan-binding lectin-associated serine proteases-1 and -2.
Mannan-binding lectin (MBL)-associated serine proteases-1 and 2 (MASP-1 and MASP-2) are homologous modular proteases that each interact with MBL, an oligomeric serum lectin involved in innate immunity. To precisely determine their substrate specificity, human MASP-1 and MASP-2, and fragments from their catalytic regions were expressed using a baculovirus/insect cells system. Recombinant MASP-2 displayed a rather wide, C1s-like esterolytic activity, and specifically cleaved complement proteins C2 and C4, with relative efficiencies 3- and 23-fold higher, respectively, than human C1s. MASP-2 also showed very weak C3 cleaving activity. Recombinant MASP-1 had a lower and more restricted esterolytic activity. It showed marginal activity toward C2 and C3, and no activity on C4. The enzymic activity of both MASP-1 and MASP-2 was specifically titrated by C1 inhibitor, and abolished at a 1:1 C1 inhibitor:protease ratio. Taken together with previous findings, these and other data strongly support the hypothesis that MASP-2 is the protease that, in association with MBL, triggers complement activation via the MBL pathway, through combined self-activation and proteolytic properties devoted to C1r and C1s in the C1 complex. In view of the very low activity of MASP-1 on C3 and C2, our data raise questions about the implication of this protease in complement activation.
Rossi
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V
Laboratoire d'Enzymologie Moléculaire, Institut de Biologie Structurale Jean-Pierre Ebel (CEA-CNRS), 41 rue Jules Horowitz, 38027 Grenoble Cedex 1, France.
Cseh
S
S
Bally
I
I
Thielens
N M
NM
Jensenius
J C
JC
Arlaud
G J
GJ
D001483:Base Sequence; D002384:Catalysis; D003167:Complement Activation; D017931:DNA Primers; D004591:Electrophoresis, Polyacrylamide Gel; D004952:Esters / Q000378:metabolism; D006801:Humans; D006868:Hydrolysis; D007700:Kinetics; D050606:Mannose-Binding Protein-Associated Serine Proteases; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism; D012697:Serine Endopeptidases / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D015842:Serine Proteinase Inhibitors / Q000494:pharmacology; D013379:Substrate Specificity
D017931:DNA Primers; D004952:Esters; D011994:Recombinant Proteins; D015842:Serine Proteinase Inhibitors; D050606:Mannose-Binding Protein-Associated Serine Proteases; D012697:Serine Endopeptidases