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Molecular cloning, overexpression in Escherichia coli, structural and functional characterization of house fly
V M Guzov1, H L Houston, M B Murataliev
1Department of Entomology, University of Arizona, Tucson, Arizona 85721, USA.
Abstract:
A microsomal cytochrome b5 cDNA from the house fly, Musca domestica, was cloned and sequenced. The deduced amino acid sequence of the full-length house fly cytochrome b5 (134 residues) is 48% identical to that of rat microsomal cytochrome b5. The house fly cytochrome b5 protein was overexpressed in Escherichia coli, purified, and characterized. Absorption and EPR spectroscopy reveal properties very similar to cytochromes b5 from vertebrates. NMR spectra indicate that the orientation of the heme in the protein relative to its alpha,gamma meso axis is about 1:1. A redox potential of -26 mV versus standard hydrogen electrode was measured by cyclic voltammetry on a modified gold electrode in the presence of hexamminechromium(III) chloride. The cytochrome b5 is reduced by house fly cytochrome P450 reductase in a reconstituted system at a high rate (5.5 s-1), and it stimulates heptachlor epoxidation when reconstituted with house fly cytochrome P450 reductase, cytochrome P450 6A1, phospholipid, and detergent. Cytochrome b5 decreases the apparent Km for P450 reductase and increases the Vmax for heptachlor epoxidation at constant cytochrome P450 6A1 concentrations. The results indicate that cytochrome b5 stimulates a step following the first electron transfer during cytochrome P450 6A1 turnover.
Insights
House fly cytochrome b5 was cloned and characterized. This protein stimulates heptachlor epoxidation by cytochrome P450 6A1, indicating a role in insect detoxification pathways.
Area of Science:
- Biochemistry
- Molecular Biology
- Insect Science
Background:
- Microsomal cytochrome b5 is a key protein in electron transfer reactions.
- Understanding insect cytochrome b5 is crucial for insecticide development and pest control.
Purpose of the Study:
- To clone, sequence, and characterize house fly (Musca domestica) microsomal cytochrome b5.
- To investigate the functional role of house fly cytochrome b5 in cytochrome P450-mediated reactions.
Main Methods:
- Cloning and sequencing of Musca domestica cytochrome b5 cDNA.
- Overexpression in E. coli, purification, and characterization using spectroscopy (absorption, EPR, NMR).
- Electrochemical analysis (cyclic voltammetry) and functional reconstitution assays with cytochrome P450 reductase and P450 6A1.
Main Results:
- House fly cytochrome b5 shares structural and spectral properties with vertebrate counterparts.
- The protein was successfully overexpressed, purified, and its redox potential determined.
- Cytochrome b5 significantly stimulates heptachlor epoxidation by P450 6A1, altering kinetic parameters (Km and Vmax).
Conclusions:
- House fly cytochrome b5 is functionally similar to vertebrate forms.
- It plays a stimulatory role in cytochrome P450 6A1 activity, likely after the initial electron transfer step.
- This finding has implications for understanding insect metabolism and developing targeted pesticides.