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Structural and kinetic evidence for strain in biological catalysis
F E Romesberg1, B D Santarsiero, B Spiller
1Howard Hughes Medical Institute, Department of Chemistry, University of California, Berkeley 94720, USA.
Biochemistry
|October 17, 1998
Summary
This study reveals how an antibody metal chelatase uses substrate strain to catalyze reactions. This mechanism, involving a distorted porphyrin, likely evolved during antibody affinity maturation.
Area of Science:
- Biochemistry
- Structural Biology
- Immunology
Background:
- Enzyme catalysis often involves substrate strain, a concept dating back to Haldane's lock and key analogy.
- This strain mechanism has been proposed for enzyme efficiency but lacks conclusive evidence.
- Antibody catalysis offers a unique system to study enzyme mechanisms.
Purpose of the Study:
- To investigate the role of substrate strain in antibody-catalyzed metal ion insertion into porphyrins.
- To provide structural and functional evidence for the strain mechanism in a specific antibody metal chelatase.
Main Methods:
- X-ray crystallography was used to determine the structure of the antibody metal chelatase.
- Mutational studies were performed to probe the catalytic mechanism.
- Analysis of the germline precursor antibody provided evolutionary insights.
Main Results:
- Structural and mutational data strongly support a strain-induction mechanism in the antibody metal chelatase.
- The antibody appears to catalyze metal ion insertion into the porphyrin ring by inducing strain.
- The germline precursor suggests this strain mechanism evolved during affinity maturation.
Conclusions:
- Antibody metal chelatase employs a strain mechanism for catalysis, supporting a classic hypothesis.
- This mechanism likely arose in response to a conformationally distorted substrate (N-alkylmesoporphyrin).
- The study provides a compelling example of antibody-driven catalytic strategy and evolution.