Palmitoylation-Induced Conformational-Changes of Specific Side-Chains in the Gramicidin Transmembrane Channel
by Koeppe II, R. Erdman; Killian, Josephine Antoinette; Bas Vogt, T. C.; De Kruijff, Ben; Taylor, Martin Jeffrey; Mattice, Gwendolyn L.; Greathouse, Denise V.
TO gain insight into the structural consequences of acylation for membrane proteins, we have covalently attached palmitic acid to the ethanolamine end of gramicidin A (gA), which functions as a well-characterized cation-selective membrane channel. Next, we investigated by NMR methods the effect of acylation on the side chains of Trp(9), Leu(10), and Trp(11), which are expected to be close to the acyl chain, and of Val(7), which is expected to be far from the acyl chain. Two-dimensional NMR spectroscopy in a sodium dodecyl sulfate (SDS) environment suggests that one of the beta-hydrogens of Leu(10) of gA is severely shielded by a nearby aromatic ring. This shielding disappears upon acylation. Deuterium NMR spectra for labeled samples in hydrated dimyristoylphosphatidylcholine (DMPC) bilayers show that, for the major gA conformation, the (deuterated) side chains of Trp(9) and Leu(10) are markedly influenced by acylation, whereas the side chains of Val(7) and Trp(11) are essentially unaffected, The NMR results in both environments suggest that the indole ring of Trp(9) is situated near the side chain of Leu(10) and moves away upon acylation, We propose that acylation provides a subtle mechanism to modulate protein and lipid interactions and to regulate the stability and function of proteins within membranes.
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