title: The structure of the Arabidopsis thaliana SOS3: molecular mechanism of sensing calcium for salt stress response.
abstract: The Arabidopsis thaliana SOS3 gene encodes a calcium sensor that is required for plant salt tolerance. The SOS3 protein binds to and activates the self-inhibited SOS2 protein kinase, which mediates the expression and activities of various transporters important for ion homeostasis under salt stress. SOS3 belongs to a unique family of calcium-binding proteins that contain two pairs of EF hand motifs with four putative metal-binding sites. We report the crystal structure of a dimeric SOS3 protein in complex with calcium, and with calcium and manganese. Analytical ultracentrifugation experiments and circular dichroism measurements show that calcium binding is responsible for the dimerization of SOS3. This leads to a change in the global shape and surface properties of the protein that may be sufficient to transmit the Ca(2+) signal elicited during salt stress.
authors.affiliation: Grupo de Cristalografía Macromolecular y Biología Estructural, Instituto de Química Física "Rocasolano", Consejo Superior de Investigaciones Científicas, Serrano 119, E-28006 Madrid, Spain.
authors.forename: María José
authors.initials: MJ
authors.lastname: Sánchez-Barrena
authors.forename: Martín
authors.initials: M
authors.lastname: Martínez-Ripoll
authors.forename: Jian-Kang
authors.initials: JK
authors.lastname: Zhu
authors.forename: Armando
authors.initials: A
authors.lastname: Albert
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000737:chemistry* / Q000187:drug effects / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry* / Q000378:metabolism*; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D002135:Calcium-Binding Proteins / Q000737:chemistry / Q000378:metabolism; D002147:Calmodulin / Q000737:chemistry; D002942:Circular Dichroism; D018360:Crystallography, X-Ray; D019281:Dimerization; D057927:Hydrophobic and Hydrophilic Interactions; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010935:Plant Diseases / Q000139:chemically induced*; D017510:Protein Folding; D020836:Protein Structure, Quaternary; D012492:Salts / Q000494:pharmacology*; D016415:Sequence Alignment; D012996:Solutions
chemical_list: D029681:Arabidopsis Proteins; D002118:Calcium; D002135:Calcium-Binding Proteins; D002147:Calmodulin; D012492:Salts; D012996:Solutions; C480758:At5g55990 protein, Arabidopsis; C112941:SOS3 protein, Arabidopsis