title: HAMP domain structural determinants for signalling and sensory adaptation in Tsr, the Escherichia coli serine chemoreceptor.
abstract: HAMP domains mediate input-output transactions in many bacterial signalling proteins. To clarify the mechanistic logic of HAMP signalling, we constructed Tsr-HAMP deletion derivatives and characterized their steady-state signal outputs and sensory adaptation properties with flagellar rotation and receptor methylation assays. Tsr molecules lacking the entire HAMP domain or just the HAMP-AS2 helix generated clockwise output signals, confirming that kinase activation is the default output state of the chemoreceptor signalling domain and that attractant stimuli shift HAMP to an overriding kinase-off signalling state to elicit counter-clockwise flagellar responses. Receptors with deletions of the AS1 helices, which free the AS2 helices from bundle-packing constraints, exhibited kinase-off signalling behaviour that depended on three C-terminal hydrophobic residues of AS2. We conclude that AS2/AS2' packing interactions alone can play an important role in controlling output kinase activity. Neither kinase-on nor kinase-off HAMP deletion outputs responded to sensory adaptation control, implying that out-of-range conformations or bundle-packing stabilities of their methylation helices prevent substrate recognition by the adaptation enzymes. These observations support the previously proposed biphasic, dynamic-bundle mechanism of HAMP signalling and additionally show that the structural interplay of helix-packing interactions between HAMP and the adjoining methylation helices is critical for sensory adaptation control of receptor output.
authors.affiliation: Biology Department, University of Utah, Salt Lake City, UT, 84112, USA.
authors.forename: Peter
authors.initials: P
authors.lastname: Ames
authors.forename: Qin
authors.initials: Q
authors.lastname: Zhou
authors.forename: John S
authors.initials: JS
authors.lastname: Parkinson
mesh_terms: D000222:Adaptation, Physiological; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D004926:Escherichia coli / Q000378:metabolism*; D005407:Flagella / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism*; D000072236:Methyl-Accepting Chemotaxis Proteins; D008954:Models, Biological; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D017434:Protein Structure, Tertiary; D017384:Sequence Deletion; D015398:Signal Transduction; D013329:Structure-Activity Relationship
chemical_list: D001426:Bacterial Proteins; D008565:Membrane Proteins; D000072236:Methyl-Accepting Chemotaxis Proteins; D050505:Mutant Proteins; C000607604:tsr protein, E coli