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Catalytic antibody model and mutagenesis implicate arginine in transition-state stabilization
V A Roberts1, J Stewart, S J Benkovic
1Department of Molecular Biology, Scripps Research Institute, La Jolla, CA 92037.
Journal of Molecular Biology
|January 21, 1994
Summary
Computational modeling and experiments reveal Arg L96 in catalytic antibody NPN43C9 stabilizes transition states. This residue enhances antigen binding and promotes catalysis by complementing negative charges in the transition state.
Area of Science:
- Biochemistry
- Structural Biology
- Immunology
Background:
- Catalytic antibodies accelerate chemical reactions.
- Understanding their mechanisms is crucial for designing new catalysts.
- The catalytic antibody NPN43C9's mechanism was previously unclear.
Purpose of the Study:
- To elucidate the catalytic mechanism of antibody NPN43C9.
- To investigate the role of Arg L96 in antigen binding and catalysis.
- To validate computational model predictions through experimental mutation.
Main Methods:
- Three-dimensional model construction of NPN43C9 variable region using antibody structural database (ASD).
- Analysis of conserved backbone and side-chain conformations.
- Site-directed mutagenesis to create R-L96-Q mutant.
- Experimental characterization of mutant for antigen binding and esterase activity.
Main Results:
- The NPN43C9 model identified Arg L96 at the antigen-binding site, forming a salt bridge with the antigen's phosphonamidate group.
- Arg L96 was predicted to enhance antigen binding and stabilize catalytic transition states.
- The R-L96-Q mutant showed decreased antigen binding and lost esterase activity, confirming Arg L96's role.
Conclusions:
- Arg L96 is critical for both binding and catalysis in NPN43C9.
- The antibody stabilizes high-energy transition states through electrostatic interactions mediated by Arg L96.
- Computational modeling combined with experimental validation provides a powerful approach to study catalytic antibody mechanisms.