title: Substitutions in the redox-sensing PAS domain of the NifL regulatory protein define an inter-subunit pathway for redox signal transmission.
abstract: The Per-ARNT-Sim (PAS) domain is a conserved α/β fold present within a plethora of signalling proteins from all kingdoms of life. PAS domains are often dimeric and act as versatile sensory and interaction modules to propagate environmental signals to effector domains. The NifL regulatory protein from Azotobacter vinelandii senses the oxygen status of the cell via an FAD cofactor accommodated within the first of two amino-terminal tandem PAS domains, termed PAS1 and PAS2. The redox signal perceived at PAS1 is relayed to PAS2 resulting in conformational reorganization of NifL and consequent inhibition of NifA activity. We have identified mutations in the cofactor-binding cavity of PAS1 that prevent 'release' of the inhibitory signal upon oxidation of FAD. Substitutions of conserved β-sheet residues on the distal surface of the FAD-binding cavity trap PAS1 in the inhibitory signalling state, irrespective of the redox state of the FAD group. In contrast, substitutions within the flanking A'α-helix that comprises part of the dimerization interface of PAS1 prevent transmission of the inhibitory signal. Taken together, these results suggest an inter-subunit pathway for redox signal transmission from PAS1 that propagates from core to the surface in a conformation-dependent manner requiring a flexible dimer interface.
authors.affiliation: Department of Molecular Microbiology, John Innes Centre, Norwich Research Park, Norwich NR47UH, UK.
authors.forename: Richard
authors.initials: R
authors.lastname: Little
authors.forename: Paloma
authors.initials: P
authors.lastname: Salinas
authors.forename: Peter
authors.initials: P
authors.lastname: Slavny
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Clarke
authors.forename: Ray
authors.initials: R
authors.lastname: Dixon
mesh_terms: D016948:Azotobacter vinelandii / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D019281:Dimerization; D005182:Flavin-Adenine Dinucleotide / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D010084:Oxidation-Reduction; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D015398:Signal Transduction
chemical_list: D001426:Bacterial Proteins; C084296:nifL protein, Bacteria; D005182:Flavin-Adenine Dinucleotide