Concerning P450 Evolution: Structural Analyses Support Bacterial Origin of Sterol 14α-Demethylases.

Area of Science:

• Biochemistry
• Structural Biology
• Microbiology

Background:

• Sterol biosynthesis is crucial in eukaryotes but occurs via an abbreviated pathway in the bacterium Methylococcus capsulatus.
• Sterol 14α-demethylation, an essential step, is catalyzed by cytochrome P450 51 (CYP51).
• In M. capsulatus, CYP51 is a natural fusion of P450 and ferredoxin domains (CYP51fx).

Purpose of the Study:

• To determine the structure of the bacterial sterol biosynthetic enzyme M. capsulatus CYP51fx.
• To compare the structure of bacterial CYP51fx with eukaryotic orthologs and other bacterial CYP51s.
• To investigate the evolutionary relationship between bacterial and eukaryotic CYP51 enzymes.

Main Methods:

• X-ray crystallography was used to solve the structure of M. capsulatus CYP51fx at 2.7 Å resolution.
• A second structure of the P450 domain with bound detergent was solved at 2.4 Å resolution.
• Bioinformatic analysis was performed to assess the prevalence and distribution of CYP51 genes in bacteria.

Main Results:

• The structure of M. capsulatus CYP51fx is the first of a bacterial sterol biosynthetic enzyme.
• No electron density was observed for the ferredoxin domain, suggesting substrate binding is required for its activation.
• Comparison with human, fungal, and protozoan CYP51s revealed conserved protein architecture, while an "orphan" P450 from Mycobacterium tuberculosis showed significant differences.
• Bioinformatic analysis identified CYP51 genes in over 1,000 bacterial species, with over 50 exhibiting the CYP51fx fusion.

Conclusions:

• Bacterial and eukaryotic CYP51 enzymes share a common ancestor.
• Early eukaryotes likely acquired the CYP51 gene from a bacterial source.
• The structural conservation and widespread bacterial distribution support the hypothesis of horizontal gene transfer for this essential enzyme.