title: Phosphorylation-independent activation of the atypical response regulator NblR.
abstract: Cyanobacteria respond to environmental stress conditions by adjusting their photosynthesis machinery. In Synechococcus sp. PCC 7942, phycobilisome degradation and other acclimation responses after nutrient or high-light stress require activation by the orphan response regulator NblR, a member of the OmpR/PhoB family. Although NblR contains a putative phosphorylatable residue (Asp57), it lacks other conserved residues required to chelate the Mg(2+) necessary for aspartic acid phosphorylation or to transduce the phosphorylation signal. In close agreement with these features, NblR was not phosphorylated in vitro by the low-molecular-mass phosphate donor acetyl phosphate and mutation of Asp57 to Ala had no impact on previously characterized NblR functions in Synechococcus. On the other hand, in vitro and in vivo assays show that the default state of NblR is monomeric, suggesting that, despite input differences, NblR activation could involve the same general mechanism of activation by dimerization present in known members of the OmpR/PhoB family. Structural and functional data indicate that the receiver domain of NblR shares similarities with other phosphorylation-independent response regulators such as FrzS and HP1043. To acknowledge the peculiarities of these atypical 'two-component' regulators with phosphorylation-independent signal transduction mechanisms, we propose the term PIARR, standing for phosphorylation-independent activation of response regulator.
authors.affiliation: División de Genética, Universidad de Alicante, Apartado 99, E-03080 Alicante, Spain.
authors.forename: Diego
authors.initials: D
authors.lastname: Ruiz
authors.affiliation: División de Genética, Universidad de Alicante, Apartado 99, E-03080 Alicante, Spain.
authors.forename: Paloma
authors.initials: P
authors.lastname: Salinas
authors.affiliation: Instituto de Biomedicina de Valencia (CSIC) and CIBERER, 46010 Valencia, Spain.
authors.forename: Maria Luisa
authors.initials: ML
authors.lastname: Lopez-Redondo
authors.affiliation: División de Genética, Universidad de Alicante, Apartado 99, E-03080 Alicante, Spain.
authors.forename: Maria Luisa
authors.initials: ML
authors.lastname: Cayuela
authors.affiliation: Instituto de Biomedicina de Valencia (CSIC) and CIBERER, 46010 Valencia, Spain.
authors.forename: Alberto
authors.initials: A
authors.lastname: Marina
authors.affiliation: División de Genética, Universidad de Alicante, Apartado 99, E-03080 Alicante, Spain.
authors.forename: Asunción
authors.initials: A
authors.lastname: Contreras
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002850:Chromatography, Gel; D004269:DNA, Bacterial / Q000235:genetics; D019281:Dimerization; D015180:Electrophoresis, Gel, Two-Dimensional; D015964:Gene Expression Regulation, Bacterial; D008969:Molecular Sequence Data; D010755:Organophosphates / Q000378:metabolism; D010766:Phosphorylation; D045524:Phycobilisomes / Q000378:metabolism; D010957:Plasmids; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D015398:Signal Transduction; D013329:Structure-Activity Relationship; D046940:Synechococcus / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D020798:Two-Hybrid System Techniques
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; C114424:NblR protein, Synechococcus sp.; D010755:Organophosphates; D045524:Phycobilisomes; D014157:Transcription Factors; C011632:acetyl phosphate