Engineering of proteolytically stable NADPH-cytochrome P450 reductase

Area of Science:

• Biochemistry
• Molecular Biology
• Enzymology

Background:

• NADPH-cytochrome P450 reductase (CPR) is a key flavoprotein in P450-mediated hydroxylation reactions.
• CPR's N-terminal hydrophobic sequence (residues 1-56) anchors it to the membrane but is prone to proteolysis, causing instability.
• Proteolytic cleavage at Lys56-Ile57 destabilizes CPR during purification and expression.

Purpose of the Study:

• To create a stable, full-length CPR mutant resistant to spontaneous proteolysis.
• To investigate the role of the N-terminal hydrophobic sequence in CPR's membrane interaction and electron transfer.
• To elucidate the structural topology of CPR within the membrane.

Main Methods:

• Site-directed mutagenesis to replace Lys56 with Gln, generating the Lys56Gln mutant.
• Limited proteolysis using trypsin and Staphylococcus aureus protease on wild-type and mutant CPR.
• Analysis of spectral and catalytic properties of the mutant and truncated forms.
• Electron transfer assays with P450c17 and P4503A4.

Main Results:

• The Lys56Gln mutant is stable to spontaneous proteolysis and trypsinolysis while retaining wild-type spectral and catalytic properties.
• Limited proteolysis of the mutant revealed altered cleavage patterns, suggesting partial accessibility of other sites.
• Truncated forms lacking the N-terminal sequence were unable to transfer electrons to P450s, confirming the sequence's catalytic importance.
• A structural topology model for the N-terminal hydrophobic sequence of CPR in the membrane was proposed.

Conclusions:

• The Lys56Gln mutation effectively stabilizes CPR against proteolysis without compromising its function.
• The N-terminal hydrophobic sequence is crucial for both membrane interaction and efficient electron transfer to P450 enzymes.
• The study provides insights into CPR's membrane topology and a stable tool for further research.