Conformational studies on a synthetic C-terminal fragment of the alpha subunit of G(S) proteins

It has recently been reported that synthetic peptides corresponding to the C-terminal sequence of G alpha, can be used to study the molecular mechanis ms of interaction between this protein and G protein coupled receptors (Ham m et al., Science, 1988, Vol. 241, pp. 832-835). A conformational analysis on a 11 amino acids peptide from the G alpha(S) C -terminus, G alpha(S)(384-394) (H-QRMHLRQYELL-OH), was performed by nmr spe ctroscopy and molecular modeling methods. Two-dimensional nmr spectra, reco rded in hexafluoroacetone/water, a mixture with structure stabilizing prope rties, showed an unusually high number of nuclear Overhauser effects, formi ng significative pattern to the drawing of a secondary structure. Conformat ions consistent with experimental NOE distances were obtained through molec ular dynamics and energy minimization methods. These calculations yielded t wo stable conformers corresponding to an alpha-turn mid a type III beta-tur n involving the last five C-terminal residues. Interestingly the alpha-turn conformation was found to overlap with good agreement the crystallographic structure of the same fragment in the G alpha(S) protein. (C) 2000 John Wi ley & Sons, Inc.