Conformation change of effector-region residues in antiparallel β-sheet of human c-Ha- ras protein on GDP→GTPγS exchange: A two-dimensional NMR study

Abstract

The conformations of a truncated human c-Ha- ras gene product [ ras(1–171) protein] in the GDP-bound form and in the GTPγS-bound form were compared by two-dimensional nuclear Overhauser effect spectroscopy (NOESY). As for the GDP-bound ras(1–171) protein, three NOESY cross peaks were observed in the region of 4.5–6.0 ppm, indicating a regular antiparallel β-sheet structure. On the ligand exchange from GDP to GTPγS, one of the three NOESY cross peaks disappeared and the other two cross peaks were appreciably shifted. By analysis of the effects of specific deuteration of leucine residues and the homonuclear Hartmann-Hahn spectroscopy, the antiparallel β-sheet was found to consist of residues 38–44 and residues 51–57. The conformations around Ser-39 and Leu-56 are of the regular antiparallel β-strand type in the GDP-bound state, and largely distorted in the GTPγS-bound state, which is probably related to the conformational activation of the effector region of ras proteins by ligand exchange from GDP to GTPγS.