title: Functional study on GTP hydrolysis by the GTP-binding protein from Sulfolobus solfataricus, a member of the HflX family.
abstract: GTPase domains from members of the HflX protein family have their catalytic glutamine residue of the DxxGQ motif substituted by phenylalanine, while they are still able to hydrolyse GTP. This appears to challenge the traditional view of GTP hydrolysis mechanism of Ras-like GTPases. SsGBP from the hyperthermophilic archaeon Sulfolobus solfataricus provided the first crystal structure of the HflX family. Here, we report structure-based mutagenesis analyses on SsGBP. Six-point mutations were individually introduced in the Ras-like GTPase domain including regions of P-loop, switches I and II. Intrinsic GTPase activities and thermal stabilities of these variants together with the wild-type full-length SsGBP and its isolated GTPase domain were analysed. Both functional and structural analyses of G235P and G235S mutants, which showed total and partial loss of the GTP hydrolyzing activity, respectively, support our hypothesis that the role of aligning a nucleophilic water molecule by the Ras Gln60 residue is replaced by the backbone amide group of Gly235 in SsGBP. Together with functional studies of other mutants, we conclude that the classical view of GTP hydrolysis mechanism likely remains the same in the HflX family with a twist in the entity of the nucleophilic alignment.
authors.affiliation: Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Chaoyang District, Beijing 100101, China.
authors.forename: Bo
authors.initials: B
authors.lastname: Huang
authors.forename: Hao
authors.initials: H
authors.lastname: Wu
authors.forename: Ning
authors.initials: N
authors.lastname: Hao
authors.forename: Fabian
authors.initials: F
authors.lastname: Blombach
authors.forename: John
authors.initials: J
authors.lastname: van der Oost
authors.forename: Xuemei
authors.initials: X
authors.lastname: Li
authors.forename: Xuejun C
authors.initials: XC
authors.lastname: Zhang
authors.forename: Zihe
authors.initials: Z
authors.lastname: Rao
mesh_terms: D019943:Amino Acid Substitution / Q000235:genetics; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D006153:Guanosine Diphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism*; D006868:Hydrolysis / Q000187:drug effects; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D017354:Point Mutation / Q000235:genetics; D017434:Protein Structure, Tertiary; D048229:Sulfolobus solfataricus / Q000378:metabolism*; D013997:Time Factors
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D050505:Mutant Proteins; D006153:Guanosine Diphosphate; D006160:Guanosine Triphosphate; D019204:GTP-Binding Proteins; C535071:HflX protein, E coli; D008274:Magnesium