title: cis-Active Ras G2-like sequence implicated in the heterotropic activation of the deoxyadenosine kinase of Lactobacillus acidophilus R-26.
abstract: Deoxyadenosine kinase (dAK) forms a heterodimer with either deoxyguanosine kinase (dGK) or deoxycytidine kinase (dCK), and is heterotropically activated 3-5 times by dGuo or dCyd. Expressed alone, dAK is inactive and exhibits no response to dGuo or dCyd; activity and heterotropic response are fully restored upon reassociation with dGK or dCK. However, turnover of independently expressed dGK or dCK is nearly maximal, being further activated only 50-100% upon reassociation with dAK. In neither case is the heterotropic activation due to ligand-induced heterodimer formation. A proline/alanine substitution within a dAK segment homologous to loop G2 of Ras proteins yielded a heterodimer with dAK permanently cis-activated 2-fold, with a corresponding reduction in heterotropic activation by dGuo. A chimeric dAK, with 25% of its C terminus substituted by the homologous sequence from dGK, was inactive alone, and its characteristics were unchanged in the reconstituted heterodimer. Superimposing the Pro/Ala substitution on this chimera also reduced heterotropic activation by half. Cross-linking the dimer by 1,5-difluoro-2,4-dinitrobenzene was inhibited by ATP, dATP, dGTP, and dAdo, suggesting the proximity of the active site(s) to the interface. These data suggest that dAK depends on dGK or dCK in a manner resembling the reliance of Ras upon GTPase activating protein.
authors.affiliation: Department of Biochemistry, The Ohio State University, Columbus, Ohio 43210-1292, USA.
authors.forename: S
authors.initials: S
authors.lastname: Guo
authors.forename: N
authors.initials: N
authors.lastname: Ma
authors.forename: D H
authors.initials: DH
authors.lastname: Ives
mesh_terms: D000595:Amino Acid Sequence; D017124:Conserved Sequence; D004789:Enzyme Activation / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D015971:Gene Expression Regulation, Enzymologic; D011905:Genes, ras; D007779:Lactobacillus acidophilus / Q000201:enzymology / Q000235:genetics*; D008969:Molecular Sequence Data; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000235:genetics* / Q000378:metabolism; D016415:Sequence Alignment; D018631:ras Proteins / Q000235:genetics*
chemical_list: D017853:Phosphotransferases (Alcohol Group Acceptor); C020005:deoxyadenosine kinase; D018631:ras Proteins