Structural Basis of a Novel Heme Binding Bacterial One-Component Switch.

Area of Science:

• Molecular Biology
• Protein Structure and Function
• Biochemistry

Background:

• One-component systems (OCSs) are crucial for rapid cellular responses to environmental stimuli.
• Understanding sensory protein mechanisms is key to deciphering cellular adaptation.
• FG214 is a novel putative OCS protein from *Fimbriimonas ginsengisoli*.

Purpose of the Study:

• To characterize the novel OCS protein FG214 as a potential redox or O2-regulated transcription factor.
• To elucidate the structural and functional mechanisms underlying FG214's activity.
• To explore FG214's potential as a tool for gene expression regulation and biosensing.

Main Methods:

• Spectroscopic and structural analyses (including X-ray crystallography) to determine protein conformation and heme binding.
• In vitro DNA-binding assays to identify promoter sequences and assess ligand-enhanced binding.
• In vivo experiments to investigate protein homodimerization.

Main Results:

• FG214's Per-ARNT-Sim (PAS) domain binds heme b in oxidized conditions.
• Redox changes and ligand binding induce conformational shifts, causing FG214 to transition from a monomer to a homodimer.
• Oxidation stabilizes the helix-turn-helix (HTH)-PAS interface, while reduction or ligand binding dissociates the HTH, freeing dimerization surfaces.
• FG214 demonstrates ligand-enhanced binding to an identified artificial promoter sequence.
• Proof-of-concept experiments confirm FG214's ability to homodimerize in vivo.

Conclusions:

• FG214 is a novel heme-binding PAS DNA binding protein and a potential transcription factor.
• Its monomer-dimer transition mechanism is regulated by redox state and heme ligand binding.
• FG214 represents a new class of heme-PAS signaling switches and shows promise for developing redox- or gas-sensitive biosensors.