title: Structures of regulatory machinery reveal novel molecular mechanisms controlling B. subtilis nitrogen homeostasis.
abstract: All cells must sense and adapt to changing nutrient availability. However, detailed molecular mechanisms coordinating such regulatory pathways remain poorly understood. In Bacillus subtilis, nitrogen homeostasis is controlled by a unique circuitry composed of the regulator TnrA, which is deactivated by feedback-inhibited glutamine synthetase (GS) during nitrogen excess and stabilized by GlnK upon nitrogen depletion, and the repressor GlnR. Here we describe a complete molecular dissection of this network. TnrA and GlnR, the global nitrogen homeostatic transcription regulators, are revealed as founders of a new structural family of dimeric DNA-binding proteins with C-terminal, flexible, effector-binding sensors that modulate their dimerization. Remarkably, the TnrA sensor domains insert into GS intersubunit catalytic pores, destabilizing the TnrA dimer and causing an unprecedented GS dodecamer-to-tetradecamer conversion, which concomitantly deactivates GS. In contrast, each subunit of the GlnK trimer "templates" active TnrA dimers. Unlike TnrA, GlnR sensors mediate an autoinhibitory dimer-destabilizing interaction alleviated by GS, which acts as a GlnR chaperone. Thus, these studies unveil heretofore unseen mechanisms by which inducible sensor domains drive metabolic reprograming in the model Gram-positive bacterium B. subtilis.
authors.affiliation: Department of Biochemistry, Duke University Medical Center, Durham, North Carolina 27710, USA maria.schumacher@duke.edu.
authors.forename: Maria A
authors.initials: MA
authors.lastname: Schumacher
authors.affiliation: Department of Biochemistry, Duke University Medical Center, Durham, North Carolina 27710, USA.
authors.forename: Naga Babu
authors.initials: NB
authors.lastname: Chinnam
authors.affiliation: Department of Biochemistry, Duke University Medical Center, Durham, North Carolina 27710, USA.
authors.forename: Bonnie
authors.initials: B
authors.lastname: Cuthbert
authors.affiliation: Department of Biochemistry, Duke University Medical Center, Durham, North Carolina 27710, USA.
authors.forename: Nam K
authors.initials: NK
authors.lastname: Tonthat
authors.affiliation: Department of Biochemistry, Duke University Medical Center, Durham, North Carolina 27710, USA.
authors.forename: Travis
authors.initials: T
authors.lastname: Whitfill
mesh_terms: D000595:Amino Acid Sequence; D001412:Bacillus subtilis / Q000235:genetics* / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D003460:Crystallization; D004247:DNA / Q000737:chemistry / Q000378:metabolism; D019281:Dimerization; D004789:Enzyme Activation / Q000235:genetics; D005974:Glutamate-Ammonia Ligase / Q000737:chemistry / Q000378:metabolism; D006706:Homeostasis / Q000235:genetics*; D008958:Models, Molecular; D009584:Nitrogen / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D012097:Repressor Proteins / Q000378:metabolism; D016415:Sequence Alignment
chemical_list: D001426:Bacterial Proteins; D012097:Repressor Proteins; C101458:ScgR protein, Bacillus subtilis; D004247:DNA; D005974:Glutamate-Ammonia Ligase; D009584:Nitrogen
keywords: MerR family; TnrA/GlnR family; dodecamer; glutamine synthetase; tetradecamer