title: Biphasic control logic of HAMP domain signalling in the Escherichia coli serine chemoreceptor.
abstract: HAMP domains mediate input-output communication in many bacterial signalling proteins. To explore the dynamic bundle model of HAMP signalling (Zhou et al., Mol. Microbiol. 73: 801, 2009), we characterized the signal outputs of 118 HAMP missense mutants of the serine chemoreceptor, Tsr, by flagellar rotation patterns. Receptors with proline or charged amino acid replacements at critical hydrophobic packing residues in the AS1 and AS2 HAMP helices had locked kinase-off outputs, indicating that drastic destabilization of the Tsr-HAMP bundle prevents kinase activation, both in the absence and presence of the sensory adaptation enzymes, CheB and CheR. Attractant-mimic lesions that enhance the structural stability of the HAMP bundle also suppressed kinase activity, demonstrating that Tsr-HAMP has two kinase-off output states at opposite extremes of its stability range. HAMP mutants with locked-on kinase outputs appeared to have intermediate bundle stabilities, implying a biphasic relationship between HAMP stability and kinase activity. Some Tsr-HAMP mutant receptors exhibited reversed output responses to CheB and CheR action that are readily explained by a biphasic control logic. The findings of this study provide strong support for a three-state dynamic bundle model of HAMP signalling in Tsr, and possibly in other bacterial transducers as well.
authors.affiliation: Biology Department, University of Utah, Salt Lake City, Utah 84112, USA.
authors.forename: Qin
authors.initials: Q
authors.lastname: Zhou
authors.forename: Peter
authors.initials: P
authors.lastname: Ames
authors.forename: John S
authors.initials: JS
authors.lastname: Parkinson
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D004252:DNA Mutational Analysis; D004926:Escherichia coli / Q000201:enzymology / Q000378:metabolism / Q000502:physiology*; D005407:Flagella / Q000502:physiology; D015964:Gene Expression Regulation, Bacterial; D015971:Gene Expression Regulation, Enzymologic; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008954:Models, Biological; D008958:Models, Molecular; D009068:Movement; D050505:Mutant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D020125:Mutation, Missense; D011487:Protein Conformation; D017434:Protein Structure, Tertiary
chemical_list: D001426:Bacterial Proteins; D008565:Membrane Proteins; D050505:Mutant Proteins; C057635:Tsr protein, Bacteria