Abstract
Few reports have described in detail a true autoactivation process, where no extrinsic cleavage factors are required to initiate the autoactivation of a zymogen. Herein, we provide structural and mechanistic insight into the autoactivation of a multidomain serine protease: mannose-binding lectin-associated serine protease-2 (MASP-2), the first enzymatic component in the lectin pathway of complement activation. We characterized the proenzyme form of a MASP-2 catalytic fragment encompassing its C-terminal three domains and solved its crystal structure at 2.4 A resolution. Surprisingly, zymogen MASP-2 is capable of cleaving its natural substrate C4, with an efficiency about 10% that of active MASP-2. Comparison of the zymogen and active structures of MASP-2 reveals that, in addition to the activation domain, other loops of the serine protease domain undergo significant conformational changes. This additional flexibility could play a key role in the transition of zymogen MASP-2 into a proteolytically active form. Based on the three-dimensional structures of proenzyme and active MASP-2 catalytic fragments, we present model for the active zymogen MASP-2 complex and propose a mechanism for the autoactivation process.
Publication types
-
Comparative Study
-
Research Support, Non-U.S. Gov't
MeSH terms
-
Binding Sites
-
Calorimetry, Differential Scanning
-
Complement C4 / chemistry
-
Complement C4 / isolation & purification
-
Complement C4 / metabolism
-
Crystallography, X-Ray
-
Enzyme Activation
-
Enzyme Stability
-
Half-Life
-
Hydrogen Bonding
-
Hydrophobic and Hydrophilic Interactions
-
Kinetics
-
Mannose-Binding Lectin / metabolism*
-
Mannose-Binding Protein-Associated Serine Proteases / chemistry*
-
Mannose-Binding Protein-Associated Serine Proteases / genetics
-
Mannose-Binding Protein-Associated Serine Proteases / isolation & purification
-
Mannose-Binding Protein-Associated Serine Proteases / metabolism*
-
Models, Biological
-
Models, Molecular
-
Mutagenesis, Site-Directed
-
Mutation
-
Protein Binding
-
Protein Conformation
-
Protein Folding
-
Protein Structure, Secondary
-
Protein Structure, Tertiary
-
Recombinant Proteins / chemistry
-
Recombinant Proteins / isolation & purification
-
Recombinant Proteins / metabolism
-
Serine Endopeptidases / chemistry*
-
Serine Endopeptidases / metabolism*
-
Thermolysin / pharmacology
Substances
-
Complement C4
-
Mannose-Binding Lectin
-
Recombinant Proteins
-
MASP2 protein, human
-
Mannose-Binding Protein-Associated Serine Proteases
-
Serine Endopeptidases
-
Thermolysin