title: Coevolved Mutations Reveal Distinct Architectures for Two Core Proteins in the Bacterial Flagellar Motor.
abstract: Switching of bacterial flagellar rotation is caused by large domain movements of the FliG protein triggered by binding of the signal protein CheY to FliM. FliG and FliM form adjacent multi-subunit arrays within the basal body C-ring. The movements alter the interaction of the FliG C-terminal (FliGC) "torque" helix with the stator complexes. Atomic models based on the Salmonella entrovar C-ring electron microscopy reconstruction have implications for switching, but lack consensus on the relative locations of the FliG armadillo (ARM) domains (amino-terminal (FliGN), middle (FliGM) and FliGC) as well as changes during chemotaxis. The generality of the Salmonella model is challenged by the variation in motor morphology and response between species. We studied coevolved residue mutations to determine the unifying elements of switch architecture. Residue interactions, measured by their coevolution, were formalized as a network, guided by structural data. Our measurements reveal a common design with dedicated switch and motor modules. The FliM middle domain (FliMM) has extensive connectivity most simply explained by conserved intra and inter-subunit contacts. In contrast, FliG has patchy, complex architecture. Conserved structural motifs form interacting nodes in the coevolution network that wire FliMM to the FliGC C-terminal, four-helix motor module (C3-6). FliG C3-6 coevolution is organized around the torque helix, differently from other ARM domains. The nodes form separated, surface-proximal patches that are targeted by deleterious mutations as in other allosteric systems. The dominant node is formed by the EHPQ motif at the FliMMFliGM contact interface and adjacent helix residues at a central location within FliGM. The node interacts with nodes in the N-terminal FliGc α-helix triad (ARM-C) and FliGN. ARM-C, separated from C3-6 by the MFVF motif, has poor intra-network connectivity consistent with its variable orientation revealed by structural data. ARM-C could be the convertor element that provides mechanistic and species diversity.
authors.affiliation: Department of Computer Science and Synthetic Biology Theme, Brunel University London, Uxbridge UB8 3PH, United Kingdom.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Pandini
authors.affiliation: Mathematical Biology, Francis Crick Institute, Ridgeway, Mill Hill, London NW7 1AA, United Kingdom.
authors.forename: Jens
authors.initials: J
authors.lastname: Kleinjung
authors.affiliation: Department of Biochemistry, McGill University, Montreal, QC H3G 1Y6, Canada.
authors.forename: Shafqat
authors.initials: S
authors.lastname: Rasool
authors.affiliation: Molecular Biology Consortium, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, United States of America.
authors.forename: Shahid
authors.initials: S
authors.lastname: Khan
mesh_terms: D000465:Algorithms; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D003198:Computer Simulation; D018360:Crystallography, X-Ray; D019143:Evolution, Molecular; D005407:Flagella / Q000737:chemistry / Q000235:genetics* / Q000502:physiology; D008957:Models, Genetic; D008958:Models, Molecular; D009154:Mutation; D010802:Phylogeny; D011485:Protein Binding; D060066:Protein Interaction Maps; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012475:Salmonella / Q000235:genetics / Q000378:metabolism / Q000502:physiology
chemical_list: D001426:Bacterial Proteins; C075660:Flig protein, Bacteria; C066821:FliM protein, Bacteria