title: A monovalent cation acts as structural and catalytic cofactor in translational GTPases.
abstract: Translational GTPases are universally conserved GTP hydrolyzing enzymes, critical for fidelity and speed of ribosomal protein biosynthesis. Despite their central roles, the mechanisms of GTP-dependent conformational switching and GTP hydrolysis that govern the function of trGTPases remain poorly understood. Here, we provide biochemical and high-resolution structural evidence that eIF5B and aEF1A/EF-Tu bound to GTP or GTPγS coordinate a monovalent cation (M(+)) in their active site. Our data reveal that M(+) ions form constitutive components of the catalytic machinery in trGTPases acting as structural cofactor to stabilize the GTP-bound "on" state. Additionally, the M(+) ion provides a positive charge into the active site analogous to the arginine-finger in the Ras-RasGAP system indicating a similar role as catalytic element that stabilizes the transition state of the hydrolysis reaction. In sequence and structure, the coordination shell for the M(+) ion is, with exception of eIF2γ, highly conserved among trGTPases from bacteria to human. We therefore propose a universal mechanism of M(+)-dependent conformational switching and GTP hydrolysis among trGTPases with important consequences for the interpretation of available biochemical and structural data.
authors.affiliation: Abteilung für Molekulare Strukturbiologie, Institut für Mikrobiologie und Genetik Göttinger Zentrum für Molekulare Biowissenschaften Georg-August-Universität Göttingen, Göttingen, Germany bkuhle@gwdg.de.
authors.forename: Bernhard
authors.initials: B
authors.lastname: Kuhle
authors.affiliation: Abteilung für Molekulare Strukturbiologie, Institut für Mikrobiologie und Genetik Göttinger Zentrum für Molekulare Biowissenschaften Georg-August-Universität Göttingen, Göttingen, Germany.
authors.forename: Ralf
authors.initials: R
authors.lastname: Ficner
mesh_terms: D020134:Catalytic Domain; D002414:Cations, Monovalent / Q000737:chemistry / Q000378:metabolism; D003067:Coenzymes / Q000737:chemistry* / Q000378:metabolism; D018360:Crystallography, X-Ray; D015852:Eukaryotic Initiation Factor-2 / Q000737:chemistry* / Q000378:metabolism; D039642:Eukaryotic Initiation Factors / Q000737:chemistry* / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D008670:Metals / Q000737:chemistry* / Q000378:metabolism; D010444:Peptide Elongation Factor Tu / Q000737:chemistry* / Q000378:metabolism
chemical_list: D002414:Cations, Monovalent; D003067:Coenzymes; D015852:Eukaryotic Initiation Factor-2; D039642:Eukaryotic Initiation Factors; D008670:Metals; C451459:eukaryotic initiation factor-5B; D006160:Guanosine Triphosphate; D010444:Peptide Elongation Factor Tu
keywords: GTPase; catalytic mechanism; crystal structure; monovalent cation; translation