The Bacillus subtilis cytochrome-c oxidase. Variations on a conserved protein theme

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Bacillus subtilis is a Gram-positive bacterium with a complex respiratory system.
• Cytochrome-c oxidases are crucial terminal oxidases in aerobic respiration.
• Understanding the genetic basis of these enzymes is key to elucidating bacterial energy metabolism.

Purpose of the Study:

• To isolate and sequence the structural genes encoding cytochrome-c oxidase in Bacillus subtilis.
• To characterize the subunits and their predicted structural features.
• To compare the B. subtilis enzyme with other known cytochrome oxidases.

Main Methods:

• Gene isolation and DNA sequencing.
• Bioinformatic analysis of gene sequences.
• Comparative analysis of predicted protein structures.

Main Results:

• Five closely spaced genes (ctaB-F) encoding cytochrome-c oxidase subunits were identified.
• Subunits I, II, III, and IVB are encoded by ctaC-F, with ctaB potentially encoding an assembly factor.
• Structural comparisons suggest a closer relationship to the E. coli cytochrome-bo complex than to the P. denitrificans enzyme.
• Subunit II possesses a novel C-terminal cytochrome-c domain, and subunit III shows N-terminal modifications compared to mitochondrial counterparts.
• A novel subunit IVB was identified.
• The identified genes do not encode the previously isolated cytochrome aa3 from B. subtilis, indicating the presence of two distinct enzymes.

Conclusions:

• The genetic organization and subunit structure of Bacillus subtilis cytochrome-c oxidase provide insights into bacterial respiratory evolution.
• The enzyme exhibits unique structural features, including a novel cytochrome-c domain and subunit IVB.
• The findings suggest the existence of at least two distinct cytochrome-aa3-type oxidases in B. subtilis.