title: A structural model of anti-anti-σ inhibition by a two-component receiver domain: the PhyR stress response regulator.
abstract: PhyR is a hybrid stress regulator conserved in α-proteobacteria that contains an N-terminal σ-like (SL) domain and a C-terminal receiver domain. Phosphorylation of the receiver domain is known to promote binding of the SL domain to an anti-σ factor. PhyR thus functions as an anti-anti-σ factor in its phosphorylated state. We present genetic evidence that Caulobacter crescentus PhyR is a phosphorylation-dependent stress regulator that functions in the same pathway as σ(T) and its anti-σ factor, NepR. Additionally, we report the X-ray crystal structure of PhyR at 1.25 Å resolution, which provides insight into the mechanism of anti-anti-σ regulation. Direct intramolecular contact between the PhyR receiver and SL domains spans regions σ₂ and σ₄, likely serving to stabilize the SL domain in a closed conformation. The molecular surface of the receiver domain contacting the SL domain is the structural equivalent of α4-β5-α5, which is known to undergo dynamic conformational change upon phosphorylation in a diverse range of receiver proteins. We propose a structural model of PhyR regulation in which receiver phosphorylation destabilizes the intramolecular interaction between SL and receiver domains, thereby permitting regions σ₂ and σ₄ in the SL domain to open about a flexible connector loop and bind anti-σ factor.
authors.affiliation: Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL, USA. The Committee on Microbiology, The University of Chicago, Chicago, IL, USA.
authors.forename: Julien
authors.initials: J
authors.lastname: Herrou
authors.forename: Robert
authors.initials: R
authors.lastname: Foreman
authors.forename: Aretha
authors.initials: A
authors.lastname: Fiebig
authors.forename: Sean
authors.initials: S
authors.lastname: Crosson
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000502:physiology*; D016935:Caulobacter crescentus / Q000235:genetics / Q000502:physiology*; D003001:Cloning, Molecular; D018360:Crystallography, X-Ray; D015964:Gene Expression Regulation, Bacterial; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010766:Phosphorylation; D012329:RNA, Bacterial / Q000235:genetics; D016415:Sequence Alignment; D012808:Sigma Factor / Q000235:genetics / Q000502:physiology*; D013312:Stress, Physiological; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D012329:RNA, Bacterial; D012808:Sigma Factor