title: Crystal structure of the GTP-binding protein Obg from Thermus thermophilus HB8.
abstract: Obg comprises a unique family of high-molecular mass GTPases conserved from bacteria to eukaryotes. Bacterial Obg is essential for cellular growth, sporulation, and differentiation. Here, we report the crystal structure of the full-length form of Obg from Thermus thermophilus HB8 at 2.07 A resolution, in the nucleotide-free state. It reveals a three-domain arrangement, composed of the N-terminal domain, the guanine nucleotide-binding domain (G domain), and the C-terminal domain. The N-terminal and G domains have the Obg fold and the Ras-like fold, respectively. These global folds are similar to those of the recently published structure of the C-terminal domain-truncated form of Obg from Bacillus subtilis. On the other hand, the C-terminal domain of Obg was found to have a novel fold (the OCT fold). A comparison of the T.thermophilus and B.subtilis nucleotide-free Obg structures revealed significant conformational changes in the switch-I and switch-II regions of the G domain. Notably, the N-terminal domain is rotated drastically, by almost 180 degrees, around the G domain axis. In the T.thermophilus Obg crystal, the nucleotide-binding site of the G domain interacts with the C-terminal domain of the adjacent molecule. These data suggest a possible domain rearrangement of Obg, and a potential role of the C-terminal domain in the regulation of the nucleotide-binding state.
authors.affiliation: RIKEN Genomic Sciences Center, 1-7-22 Suehiro-cho, Tsurumi, Yokohama 230-0045, Japan.
authors.forename: Mutsuko
authors.initials: M
authors.lastname: Kukimoto-Niino
authors.forename: Kazutaka
authors.initials: K
authors.lastname: Murayama
authors.forename: Mio
authors.initials: M
authors.lastname: Inoue
authors.forename: Takaho
authors.initials: T
authors.lastname: Terada
authors.forename: Jeremy R H
authors.initials: JR
authors.lastname: Tame
authors.forename: Seiki
authors.initials: S
authors.lastname: Kuramitsu
authors.forename: Mikako
authors.initials: M
authors.lastname: Shirouzu
authors.forename: Shigeyuki
authors.initials: S
authors.lastname: Yokoyama
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry*; D018360:Crystallography, X-Ray; D019204:GTP-Binding Proteins / Q000737:chemistry*; D008958:Models, Molecular; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D040681:Structural Homology, Protein; D016963:Thermus thermophilus / Q000737:chemistry*
chemical_list: D001426:Bacterial Proteins; C090542:Obg GTP-binding protein, Bacteria; D019204:GTP-Binding Proteins