Functional and structural characterisation of a viral cytochrome b5

Area of Science:

• Biochemistry
• Virology
• Structural Biology

Background:

• Cytochrome b5 is a key electron transport protein in eukaryotes.
• The OtV-2 virus, infecting Ostreococcus tauri, was predicted to encode a cytochrome b5.
• Viral gene products offer insights into host-pathogen interactions and novel biological functions.

Purpose of the Study:

• To characterize the OtV-2 cytochrome b5 enzyme.
• To determine its functional and structural properties.
• To investigate its potential role in viral infection and cellular metabolism.

Main Methods:

• Purification and spectral analysis of OtV-2 cytochrome b5.
• Functional assay using yeast cytochrome P450 51 and sterol 14α-demethylation.
• X-ray crystallography to determine the enzyme's structure.

Main Results:

• OtV-2 cytochrome b5 exhibits spectral properties identical to human cytochrome b5.
• The viral enzyme functionally complements yeast cytochrome b5 in sterol demethylation.
• The crystal structure reveals a single-domain protein similar to eukaryotic cytochrome b5, but lacking a C-terminal anchor, indicating a cytosolic localization.

Conclusions:

• OtV-2 cytochrome b5 is the first characterized cytosolic cytochrome b5, likely acquired via horizontal gene transfer.
• Its unique structure and localization suggest a novel function for the virus during infection.
• This finding highlights the importance of cytochrome b5 in cellular metabolism at extreme scales.