Structural basis of Redox-coupled protein substrate selection by the cytochrome c biosynthesis protein ResA

Area of Science:

• Biochemistry
• Structural Biology
• Microbiology

Background:

• Post-translational maturation of cytochromes c necessitates heme attachment to a specific motif (Cys-Xxx-Xxx-Cys-His).
• The two cysteine residues within this motif must be in a reduced state for heme attachment.
• Bacterial thiol-disulfide oxidoreductases, essential for cytochrome c maturation, maintain this reduced state and are linked to cellular disulfide bond formation.

Purpose of the Study:

• To elucidate the structural basis of the high reducing power of the oxidoreductase ResA.
• To understand the redox-coupled conformational changes in ResA and their impact on substrate binding.
• To investigate the role of ResA's structural features in the specificity of cytochrome c maturation.

Main Methods:

• High-resolution structural determination of oxidized and reduced states of a soluble, functional domain of ResA from Bacillus subtilis.
• Analysis of structural differences between oxidized and reduced states to identify redox-coupled conformational changes.

Main Results:

• Revealed the structural basis for ResA's high reducing power.
• Observed the largest redox-coupled conformational changes to date in a thioredoxin-like protein.
• Demonstrated how these conformational changes alter the protein surface, influencing substrate binding specificity, and identified a polar cavity unique to the reduced state potentially for apo-cytochrome c recognition.

Conclusions:

• The structural dynamics of ResA are crucial for its function in cytochrome c maturation.
• The observed redox-coupled conformational changes provide insights into substrate recognition mechanisms.
• The features of ResA are likely representative of oxidoreductases involved in bacterial cytochrome c maturation systems.