title: Crystal structure of the C-terminal clock-oscillator domain of the cyanobacterial KaiA protein.
abstract: KaiA, KaiB and KaiC constitute the circadian clock machinery in cyanobacteria, and KaiA activates kaiBC expression whereas KaiC represses it. Here we show that KaiA is composed of three functional domains, the N-terminal amplitude-amplifier domain, the central period-adjuster domain and the C-terminal clock-oscillator domain. The C-terminal domain is responsible for dimer formation, binding to KaiC, enhancing KaiC phosphorylation and generating the circadian oscillations. The X-ray crystal structure at a resolution of 1.8 A of the C-terminal clock-oscillator domain of KaiA from the thermophilic cyanobacterium Thermosynechococcus elongatus BP-1 shows that residue His270, located at the center of a KaiA dimer concavity, is essential to KaiA function. KaiA binding to KaiC probably occurs via the concave surface. On the basis of the structure, we predict the structural roles of the residues that affect circadian oscillations.
authors.affiliation: Center for Gene Research, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan.
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Uzumaki
authors.forename: Masayasu
authors.initials: M
authors.lastname: Fujita
authors.forename: Toru
authors.initials: T
authors.lastname: Nakatsu
authors.forename: Fumio
authors.initials: F
authors.lastname: Hayashi
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Shibata
authors.forename: Noriyo
authors.initials: N
authors.lastname: Itoh
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Kato
authors.forename: Masahiro
authors.initials: M
authors.lastname: Ishiura
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry*; D056925:Circadian Rhythm Signaling Peptides and Proteins; D000458:Cyanobacteria / Q000737:chemistry*; D019281:Dimerization; D008163:Luminescent Measurements; D008969:Molecular Sequence Data; D010766:Phosphorylation; D011487:Protein Conformation; D017386:Sequence Homology, Amino Acid
chemical_list: D001426:Bacterial Proteins; D056925:Circadian Rhythm Signaling Peptides and Proteins; C114269:KaiA protein, cyanobacteria