title: Crystal structures of two cyanobacterial response regulators in apo- and phosphorylated form reveal a novel dimerization motif of phytochrome-associated response regulators.
abstract: The structures of two response regulators (RRs) from the cyanobacterium Calothrix PCC7601, RcpA and RcpB, were solved to 1.9- and 1.75-A resolution, respectively. RcpA was found in phosphorylated and RcpB in nonphosphorylated form. Both RRs are members of phytochrome-associated, light-sensing two-component signal transduction pathways, based on histidine kinase-mediated receptor autophosphorylation and phosphorelay to a RR. Despite the overall folding similarity to CheY-type RRs ((beta/alpha)(5)-motif), RcpA and RcpB form homodimers, irrespective of their phosphorylation state, giving insight into a signal transduction putatively different from that of other known RRs. Dimerization is accomplished by a C-terminal extension of the RR polypeptide chain, and the surface formed by H4, beta 5, and H5, which constitute a hydrophobic contact area with distinct interactions between residues of either subunit. Sequence alignments reveal that the identified dimerization motif is archetypal for phytochrome-associated RRs, making them a novel subgroup of CheY-type RRs. The protein structures of RcpA and RcpB are compared to the recently presented protein structure of Rcp1 from Synechocystis.
authors.affiliation: Max-Planck-Institut für Biochemie, D-82152 Martinsried, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Benda
authors.forename: C
authors.initials: C
authors.lastname: Scheufler
authors.forename: N
authors.initials: N
authors.lastname: Tandeau de Marsac
authors.forename: W
authors.initials: W
authors.lastname: Gärtner
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry*; D018360:Crystallography, X-Ray; D000458:Cyanobacteria; D019281:Dimerization; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010766:Phosphorylation; D010786:Photoreceptor Cells / Q000737:chemistry*; D016415:Sequence Alignment; D015398:Signal Transduction / Q000502:physiology*
chemical_list: D001426:Bacterial Proteins