title: Hyperthermostable protein structure maintained by intra and inter-helix ion-pairs in archaeal O6-methylguanine-DNA methyltransferase.
abstract: The crystal structure of O6-methylguanine-DNA methyltransferase (EC 2.1.1.63) of hyperthermophilic archaeon Pyrococcuskodakaraensis strain KOD1 (Pk -MGMT) was determined by single isomorphous replacement method with anomalous scattering (SIRAS) at 1.8 A resolution. The archaeal protein is extremely thermostable and repairs alkylated DNA by suicidal alkyl transfer from guanine O6 to its own cysteine residue. Archaea constitute the third primary kingdom of living organisms, sharing characteristics with procaryotic and eucaryotic cells. They live in various extreme environments and are thought to include the most ancient organisms on the earth. Structural studies on hyperthermophilic archaeal proteins reveal the structural features essential for stability under the extreme environments in which these organisms live, and will provide the structural basis required for stabilizing various mesophilic proteins for industrial applications. Here, we report the crystal structure of Pk-MGMT and structural comparison of Pk-MGMT and methyltransferase homologue from Escherichia coli (AdaC, C-terminal fragment of Ada protein). Analyses of solvent-accessible surface area (SASA) reveals a large discrepancy between Pk-MGMT and AdaC with respect to the property of the ASA. In the Pk-MGMT structure, the intra-helix ion-pairs contribute to reinforce stability of alpha-helices. The inter-helix ion-pairs exist in the interior of Pk-MGMT and stabilize internal packing of tertiary structure. Furthermore, structural features of helix cappings, intra and inter-helix ion-pairs are found around the active-site structure in Pk-MGMT.
authors.affiliation: Department of Materials Chemistry, Graduate School of Engineering, Osaka University, Suita, 565-0871, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Hashimoto
authors.forename: T
authors.initials: T
authors.lastname: Inoue
authors.forename: M
authors.initials: M
authors.lastname: Nishioka
authors.forename: S
authors.initials: S
authors.lastname: Fujiwara
authors.forename: M
authors.initials: M
authors.lastname: Takagi
authors.forename: T
authors.initials: T
authors.lastname: Imanaka
authors.forename: Y
authors.initials: Y
authors.lastname: Kai
mesh_terms: D000595:Amino Acid Sequence; D019843:Archaeal Proteins / Q000737:chemistry; D001426:Bacterial Proteins / Q000737:chemistry; D001665:Binding Sites; D018360:Crystallography, X-Ray; D004795:Enzyme Stability; D004926:Escherichia coli; D029968:Escherichia coli Proteins; D006358:Hot Temperature; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019853:O(6)-Methylguanine-DNA Methyltransferase / Q000737:chemistry*; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D019711:Pyrococcus / Q000201:enzymology*; D016415:Sequence Alignment; D014157:Transcription Factors
chemical_list: D019843:Archaeal Proteins; D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D014157:Transcription Factors; C045675:Ada protein, E coli; D019853:O(6)-Methylguanine-DNA Methyltransferase