Novel heme-based oxygen sensor with a revealing evolutionary history

Area of Science:

• Biochemistry
• Molecular Biology
• Microbiology

Background:

• Cells utilize sensory proteins with heme cofactors to detect oxygen concentration changes.
• Oxygen sensing is crucial for cellular processes and gene regulation.

Purpose of the Study:

• To identify and characterize a new class of heme-binding oxygen sensors.
• To elucidate the sensing mechanism of the AppA protein from Rhodobacter sphaeroides.
• To investigate the phylogenetic origins of these novel sensors.

Main Methods:

• Non-covalent heme binding assays with the AppA protein.
• Oxygen titration experiments to observe heme coordination changes.
• Transcriptional analysis of photosynthesis genes regulated by AppA and PpsR.
• Phylogenetic analysis of the newly identified SCHIC domain.

Main Results:

• Heme binds non-covalently to the central region of AppA.
• Oxygen addition discoordinates heme in AppA, with response proportional to oxygen levels.
• The AppA-PpsR system acts as an oxygen-dependent transcriptional rheostat, modulating photosynthesis gene expression.
• A new heme-binding domain, SCHIC, was identified in AppA, with distinct phylogenetic links to vitamin B12-binding proteins.

Conclusions:

• AppA functions as a novel heme-based oxygen sensor.
• The AppA-PpsR system provides a graded transcriptional response to oxygen.
• The SCHIC domain represents a new class of heme-binding domains with unique evolutionary origins.