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Modeling an Enzyme Active Site using Molecular Visualization Freeware
Published on: December 25, 2021
The cytochrome P-450cam binding surface as defined by site-directed mutagenesis and electrostatic modeling
1Department of Biochemistry, University of Illinois, Urbana 61801.
Biochemistry
|August 14, 1990
Summary
Site-directed mutagenesis of cytochrome P-450cam identified key cationic residues, Lys 344 and Arg 72, critical for putidaredoxin electron transfer. Altering these charges significantly impacted enzyme kinetics, confirming their role in protein-protein interactions.
Area of Science:
- Biochemistry
- Enzymology
- Protein Structure-Function Relationships
Background:
- Cytochrome P-450cam plays a crucial role in electron transfer processes.
- Specific cationic surface charges, Lys 344 and Arg 72, were hypothesized to be involved in protein-protein interactions with putidaredoxin and cytochrome b5.
- Previous studies suggested these residues form salt bridge contacts in association complexes.
Purpose of the Study:
- To investigate the functional role of cationic surface charges at Lys 344 and Arg 72 in cytochrome P-450cam.
- To determine the impact of altering these charges on electron transfer kinetics with putidaredoxin.
- To provide experimental and theoretical evidence for the modeled binding site interactions.
Main Methods:
- Site-directed mutagenesis was employed to alter specific cationic residues (Lys 344, Arg 72, Lys 392).
- Mutations included charge neutralization (Q) and charge reversal (E).
- NADH oxidation rates in reconstituted electron-transfer systems were measured to assess enzyme activity and kinetics (Vmax, Km).
Main Results:
- Mutations at Arg 72 (R72Q) and Lys 344 (K344Q, K344E) altered NADH oxidation rates, primarily affecting Km values.
- The K344Q and K344E mutants showed altered Km values consistent with changes in salt bridge interactions.
- A control mutation at Lys 392 (K392Q), distant from the proposed interaction site, did not significantly affect overall activity.
- Electrostatic field calculations revealed a positive potential patch at the modeled cytochrome b5 interaction site.
Conclusions:
- Cationic residues Lys 344 and Arg 72 are essential for efficient putidaredoxin-cytochrome P-450cam electron transfer.
- The observed kinetic alterations suggest these residues mediate salt bridge interactions crucial for complex formation and function.
- Experimental and theoretical data support the modeled binding site's role in interactions with both cytochrome b5 and putidaredoxin.
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