Cholesterol ester oxidation by mycobacterial cytochrome P450

Area of Science:

• Biochemistry
• Microbiology
• Enzymology

Background:

• Mycobacteria degrade cholesterol via cytochrome P450 (CYP) enzymes.
• CYP families 125 and 142 initiate cholesterol side chain oxidation.

Purpose of the Study:

• To investigate the structural and functional differences between CYP125 and CYP142 enzymes in cholesterol ester oxidation.
• To understand the enzymatic basis for differential substrate utilization in mycobacteria.

Main Methods:

• Comparative sequence and structural analysis of CYP125 and CYP142 families.
• Catalytic assays using cholesteryl propionate and cholesteryl sulfate.
• X-ray crystallography of CYP142A2 in complex with cholesteryl sulfate.

Main Results:

• CYP142 enzymes efficiently oxidize cholesteryl propionate, while CYP125 enzymes show low efficiency with cholesteryl sulfate.
• Structural analysis reveals insertions in CYP125 potentially hindering cholesterol ester oxidation.
• CYP142 possesses a compact active site facilitating efficient cholesteryl ester oxidation.

Conclusions:

• Enzyme structure dictates substrate specificity in mycobacterial cholesterol metabolism.
• CYP142's active site facilitates cholesterol ester oxidation, providing a carbon source for mycobacteria.
• CYP125's larger active site may lead to uncoupled catalytic cycles with certain sterol substrates.