title: The crystal structure of plant-specific calcium-binding protein AtCBL2 in complex with the regulatory domain of AtCIPK14.
abstract: Calcium signals mediate a multitude of plant responses to external stimuli. Calcineurin B-like (CBL) proteins and their target kinases, CBL-interacting protein kinases (CIPKs), represent important relays in plant calcium signaling. CBL interacts with CIPK through a conserved motif (NAF/FISL motif) within the C-terminal regulatory domain. To better understand the functional role of the CBL-CIPK system, we determined the crystal structure of AtCBL2 in complex with the regulatory domain of AtCIPK14 at 1.2 A resolution. The NAF/FISL motif is inserted into a hydrophobic crevice within AtCBL2, accompanied by a large displacement of the helices and loop on the opposite side of the NAF/FISL motif from the C-terminal region, which shields the hydrophobic crevice in free form. Ca(2+) are coordinated within four EF hands in AtCBL2 in bound form. This calcium coordination pattern differs from that in the structure of the SOS3-SOS2 complex previously reported. Structural comparison of the two structures shows that the recognition of CBL by CIPK is performed in a similar manner, but inherent interactions confer binding affinity and specificity.
authors.affiliation: International Graduate School of Arts and Sciences, Yokohama City University, 1-7-29 Suehiro-cho, Tsurumi-ku, Yokohama, Kanagawa 230-0045, Japan.
authors.forename: Mayuko
authors.initials: M
authors.lastname: Akaboshi
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Hashimoto
authors.forename: Hanako
authors.initials: H
authors.lastname: Ishida
authors.forename: Shinya
authors.initials: S
authors.lastname: Saijo
authors.forename: Nozomu
authors.initials: N
authors.lastname: Koizumi
authors.forename: Mamoru
authors.initials: M
authors.lastname: Sato
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Shimizu
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000737:chemistry* / Q000201:enzymology; D029681:Arabidopsis Proteins / Q000737:chemistry* / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000737:chemistry*; D016384:Consensus Sequence; D018360:Crystallography, X-Ray; D020832:EF Hand Motifs; D008969:Molecular Sequence Data; D016296:Mutagenesis; D011485:Protein Binding; D011494:Protein Kinases / Q000737:chemistry*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D017434:Protein Structure, Tertiary; D013045:Species Specificity
chemical_list: D029681:Arabidopsis Proteins; D002118:Calcium; D002135:Calcium-Binding Proteins; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; C480758:At5g55990 protein, Arabidopsis; C112941:SOS3 protein, Arabidopsis; C406738:SOS2 protein, Arabidopsis; C490996:At5g01820 protein, Arabidopsis