title: Properties of a genetically engineered G domain of elongation factor Tu.
abstract: The G domain of elongation factor Tu (EF-Tu), representing the N-terminal half of the factor according to its three-dimensional model traced at high resolution, has been isolated by genetic manipulation of tufA and purified to homogeneity. The G domain, whose primary structure shares homology with the eukaryotic protein p21, is capable of supporting the basic activities of the intact molecule (guanine nucleotide binding in 1:1 molar ratio and GTPase activity). However, it is no longer exposed to the allosteric mechanisms regulating EF-Tu. The G-domain complexes with GTP and GDP display similar K'd values in the microM range, in contrast to EF-Tu that binds GDP much more tightly than GTP. Its GTPase shows the characteristics of a slow turnover reaction (0.1 mmol X sec-1 X mol-1 of G domain), whose rate closely corresponds to the initial hydrolysis rate of EF-Tu X GTP in the absence of effectors and lies in the typical range of GTPase of the p21 protein. Of the EF-Tu ligands only the ribosome displays a clear effect enhancing the G-domain GTPase. Our results suggest that the middle and C-terminal domain play an essential role in regulating the activity of the N-terminal domain of the intact molecule as well as in the interactions of EF-Tu with aminoacylated tRNA, elongation factor Ts, and kirromycin. With the isolation of the G domain of EF-Tu, a model protein has been constructed for studying and comparing common characteristics of the guanine nucleotide-binding proteins.
mesh_terms: D001665:Binding Sites; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism; D020963:GTP Phosphohydrolase-Linked Elongation Factors / Q000378:metabolism; D005818:Genetic Engineering; D006153:Guanosine Diphosphate / Q000378:metabolism; D010444:Peptide Elongation Factor Tu / Q000235:genetics* / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation
chemical_list: D006153:Guanosine Diphosphate; D020963:GTP Phosphohydrolase-Linked Elongation Factors; D010444:Peptide Elongation Factor Tu