title: Crystal structure of the conserved protein TTHA0727 from Thermus thermophilus HB8 at 1.9 A resolution: A CMD family member distinct from carboxymuconolactone decarboxylase (CMD) and AhpD.
abstract: TTHA0727 is a conserved hypothetical protein from Thermus thermophilus HB8, with a molecular mass of 12.6 kDa. TTHA0727 belongs to the carboxymuconolactone decarboxylase (CMD) family (Pfam 02627). A sequence comparison with its homologs suggested that TTHA0727 is a distinct protein from alkylhydroperoxidase AhpD and gamma-carboxymuconolactone decarboxylase in the CMD family. Here we report the 1.9 A crystal structure of TTHA0727 (PDB ID: 2CWQ) determined by the multiwavelength anomalous dispersion method. The TTHA0727 monomer structure consists of seven alpha-helices (alpha1-alpha7) and one short 3(10)-helix. The crystal structure and the analytical ultracentrifugation revealed that TTHA0727 forms a hexameric ring structure in solution. The electrostatic potential distribution on the solvent-accessible surface of the TTHA0727 hexamer showed that positively charged regions exist on the side of the ring structure, suggesting that TTHA0727 interacts with some negatively charged molecules. A structural homology search revealed that the structure of three alpha-helices (alpha4-alpha6) is remarkably conserved, suggesting that it is the common structural motif for the CMD family proteins. In addition, the nine residues of the N-terminal tag bound to the cleft region between alpha1 and alpha3 in chains A and B of TTHA0727, implying that this region is the putative binding/active site for some small molecules.
authors.affiliation: Protein Research Group, RIKEN Genomic Sciences Center, Tsurumi, Yokohama 230-0045, Japan.
authors.forename: Kaori
authors.initials: K
authors.lastname: Ito
authors.forename: Ryoichi
authors.initials: R
authors.lastname: Arai
authors.forename: Emiko
authors.initials: E
authors.lastname: Fusatomi
authors.forename: Tomomi
authors.initials: T
authors.lastname: Kamo-Uchikubo
authors.forename: Shin-Ichi
authors.initials: S
authors.lastname: Kawaguchi
authors.forename: Ryogo
authors.initials: R
authors.lastname: Akasaka
authors.forename: Takaho
authors.initials: T
authors.lastname: Terada
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; D002262:Carboxy-Lyases / Q000737:chemistry*; D003460:Crystallization; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D017386:Sequence Homology, Amino Acid; D040681:Structural Homology, Protein; D013329:Structure-Activity Relationship; D016963:Thermus thermophilus / Q000737:chemistry*
chemical_list: D002262:Carboxy-Lyases; C019832:4-carboxymuconolactone decarboxylase