Conformation of guanosine 5'-diphosphate as bound to a human c-Ha-ras mutant protein: a nuclear Overhauser effect study

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Abstract
1H NMR spectra of GDP/GTP-binding domain of human c-Ha-ras gene product (residues 1-171) in which glutamine-61 was replaced by leucine [ras(L61/1-171) protein] were analyzed. By one-dimensional and two-dimensional homonuclear Hartmann-Hahn spectroscopy and nuclear Overhauser effect (NOE) spectroscopy of the complex of the ras(L61/1-171) protein and GDP, the ribose H1'', H2'', H3'', and H4'' proton resoonances of the bound GDP were identified. The guanine H8 proton resonance of the bound GDP was identified by substituting [8-2H]GDP or GDP. The dependences of the H1'' and H8 proton resonance intensities on the duration of irradiation of the H1'', H2'', H3'', and H8 protons were measured. By numerical simulation of these time-dependent NOE profiles, the conformation of the protein-bound GDP was elucidated; the guanosine moiety takes the anti form about the N-glycosidic bond with a dihedral angle of .chi. = -124 .+-. 2.degree. and the ribose ring takes the C2''-endo form. Such an analysis of the conformation of a guanine nucleotide as bound to a GTP-binding protein will be useful for further studies on the molecular mechanism of the conformation activation of ras proteins on ligand substitution of GDP with GTP.