title: The S-helix determines the signal in a Tsr receptor/adenylyl cyclase reporter.
abstract: A signaling or S-helix has been identified as a conserved, up to 50-residue-long segment in diverse sensory proteins. It is present in all major bacterial lineages and in euryarchea and eukaryotes. A bioinformatic analysis shows that it connects upstream receiver and downstream output domains, e.g. in histidine kinases and bacterial adenylyl cyclases. The S-helix is modeled as a two-helical parallel coiled coil. It is predicted to prevent constitutive activation of the downstream signaling domains in the absence of ligand-binding. We identified an S-helix of about 25 residues in the adenylyl cyclase CyaG from Arthrospira maxima. Deletion of the 25 residue segment connecting the HAMP and catalytic domains in a chimera with the Escherichia coli Tsr receptor changed the response to serine from inhibition to stimulation. Further examination showed that a deletion of one to three heptads plus a presumed stutter, i.e. 1, 2, or 3 × 7 + 4 amino acids, is required and sufficient for signal reversion. It was not necessary that the deletions be continuous, as removal of separated heptads and presumed stutters also resulted in signal reversion. Furthermore, insertion of the above segments between the HAMP and cyclase catalytic domains similarly resulted in signal reversion. This indicates that the S-helix is an independent, segmented module capable to reverse the receptor signal. Because the S-helix is present in all kingdoms of life, e.g. in human retinal guanylyl cyclase, our findings may be significant for many sensory systems.
authors.affiliation: Pharmazeutische Biochemie, Pharmazeutisches Institut, Universität Tübingen, 72076 Tübingen, Germany.
authors.forename: Karin
authors.initials: K
authors.lastname: Winkler
authors.forename: Anita
authors.initials: A
authors.lastname: Schultz
authors.forename: Joachim E
authors.initials: JE
authors.lastname: Schultz
mesh_terms: D000262:Adenylyl Cyclases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D055162:Biocatalysis / Q000187:drug effects; D015153:Blotting, Western; D020134:Catalytic Domain; D000458:Cyanobacteria / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D012694:Serine / Q000378:metabolism / Q000494:pharmacology; D015398:Signal Transduction
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D011993:Recombinant Fusion Proteins; C057635:Tsr protein, Bacteria; D012694:Serine; D000262:Adenylyl Cyclases