title: Ability of guanine nucleotide derivatives to bind and activate bovine transducin.
abstract: Several guanine nucleotide analogs, in one series of which a hydrogen on the 2-amino group is replaced with the p-n-butylphenyl group (BuPGNP derivatives), were used to probe the GTP binding domain of bovine transducin. The order of apparent binding affinities in a series of nucleoside 5'-triphosphates was GTP gamma S greater than GTP approximately BuPGTP greater than dGTP approximately ITP much greater than ATP, values which were 30-100 times higher than affinities of the corresponding 5'-diphosphates. A derivative bearing a 6-aminohexylamino group on the gamma-phosphate, BuPGTP X C6, had a 60-fold lower affinity compared to BuPGTP. In contrast, the p-n-butylphenyl substituent on the 2-amino group had little effect on the binding affinity relative to GTP. Substitutions at the 2-amino group had little effect on either the hydrolysis of the derivatives by the GTPase activity associated with the alpha-subunit of transducin or the activation of cGMP phosphodesterase. The results indicate that the GTP binding domain of transducin is similar in tertiary structure to the corresponding domain of EF-Tu. The 5'-phosphates of GTP are oriented in the binding site of transducin so that the bulky C6 group of BuPGTP X C6 dramatically interferes with binding. The 2-amino group on the guanine ring is probably located at the periphery of the binding site, with the p-n-butylphenyl substituent of BuPGTP facing outward and only weakly interacting with the protein. BuPGTP should be an excellent parent compound for development of novel probes of G-protein interactions with other cellular proteins involved in receptor signal transduction.
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism; D006150:Guanine Nucleotides / Q000138:chemical synthesis / Q000378:metabolism* / Q000494:pharmacology; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism; D007700:Kinetics; D008565:Membrane Proteins / Q000378:metabolism*; D011485:Protein Binding; D012374:Rod Cell Outer Segment / Q000378:metabolism; D013329:Structure-Activity Relationship; D013873:Thionucleotides / Q000378:metabolism; D015293:Transducin
chemical_list: D006150:Guanine Nucleotides; D008565:Membrane Proteins; D013873:Thionucleotides; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate; D015293:Transducin