PALMITOYLATION-INDUCED CONFORMATIONAL-CHANGES OF SPECIFIC SIDE-CHAINSIN THE GRAMICIDIN TRANSMEMBRANE CHANNEL

TO gain insight into the structural consequences of acylation for memb rane proteins, we have covalently attached palmitic acid to the ethano lamine end of gramicidin A (gA), which functions as a well-characteriz ed cation-selective membrane channel. Next, we investigated by NMR met hods the effect of acylation on the side chains of Trp(9), Leu(10), an d Trp(11), which are expected to be close to the acyl chain, and of Va l(7), which is expected to be far from the acyl chain. Two-dimensional NMR spectroscopy in a sodium dodecyl sulfate (SDS) environment sugges ts that one of the beta-hydrogens of Leu(10) of gA is severely shielde d by a nearby aromatic ring. This shielding disappears upon acylation. Deuterium NMR spectra for labeled samples in hydrated dimyristoylphos phatidylcholine (DMPC) bilayers show that, for the major gA conformati on, the (deuterated) side chains of Trp(9) and Leu(10) are markedly in fluenced by acylation, whereas the side chains of Val(7) and Trp(11) a re essentially unaffected, The NMR results in both environments sugges t that the indole ring of Trp(9) is situated near the side chain of Le u(10) and moves away upon acylation, We propose that acylation provide s a subtle mechanism to modulate protein and lipid interactions and to regulate the stability and function of proteins within membranes.