title: Saccharomyces cerevisiae Ski7 Is a GTP-Binding Protein Adopting the Characteristic Conformation of Active Translational GTPases.
abstract: Ski7 is a cofactor of the cytoplasmic exosome in budding yeast, functioning in both mRNA turnover and non-stop decay (NSD), a surveillance pathway that degrades faulty mRNAs lacking a stop codon. The C-terminal region of Ski7 (Ski7C) shares overall sequence similarity with the translational GTPase (trGTPase) Hbs1, but whether Ski7 has retained the properties of a trGTPase is unclear. Here, we report the high-resolution structures of Ski7C bound to either intact guanosine triphosphate (GTP) or guanosine diphosphate-Pi. The individual domains of Ski7C adopt the conformation characteristic of active trGTPases. Furthermore, the nucleotide-binding site of Ski7C shares similar features compared with active trGTPases, notably the presence of a characteristic monovalent cation. However, a suboptimal polar residue at the putative catalytic site and an unusual polar residue that interacts with the γ-phosphate of GTP distinguish Ski7 from other trGTPases, suggesting it might function rather as a GTP-binding protein than as a GTP-hydrolyzing enzyme.
authors.affiliation: Department of Structural Cell Biology Department, Max Planck Institute of Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany.
authors.forename: Eva
authors.initials: E
authors.lastname: Kowalinski
authors.affiliation: Howard Hughes Medical Institute, Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
authors.forename: Anthony
authors.initials: A
authors.lastname: Schuller
authors.affiliation: Howard Hughes Medical Institute, Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
authors.forename: Rachel
authors.initials: R
authors.lastname: Green
authors.affiliation: Department of Structural Cell Biology Department, Max Planck Institute of Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany. Electronic address: conti@biochem.mpg.de.
authors.forename: Elena
authors.initials: E
authors.lastname: Conti
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000737:chemistry*; D000595:Amino Acid Sequence; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D020558:GTP Phosphohydrolases / Q000737:chemistry*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C118668:SKI7 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D020558:GTP Phosphohydrolases