Influence of acylation of the peptide corresponding to the amino-terminal region of endothelial Nitric Oxide Synthase on the interaction with model membranes.

Abstract

Endothelial Nitric Oxide Synthase (eNOS) is unique among the NOS isoforms in its being dually acylated by the fatty acids myristate and palmitate. Due to its N-erminus consensus sequence, eNOS becomes cotranslationally myristoylated through an amide bond between the first Gly residue and myristic acid. Interestingly, this protein can also become transiently palmitoylated through the formation of two thioester bonds at cysteine residues 15 and 26. Protein palmitoylation of previously myristoylated protein results in the membrane association of eNOS in caveolin-enriched domains. In this work we have synthesized the first 28 amino acids of eNOS i) non- cylated, ii) singly myristoylated, iii) doubly palmitoylated and iv) dually myristoylated and palmitoylated. The effect of acylation on the conformation of the peptides has been studied by means of circular dichroism and fluorescence properties of a Trp residue which has been included at position 29. Acylation with either myristic or palmitic acid confers the peptide strech the ability to adopt extended conformations. Subsequently, we have studied the interaction of these four peptides with liposomes of defined composition by means of circular dichroism and fluorescence spectroscopy and their degree of insertion within lipid vesicles measuring the polarization of diphenyl-hexatriene (DPH) and tetramethyl ammonium diphenyl-hexatriene (TMA-DPH)-labeled liposomes. The acylated peptides were able to insert deeply into the hydrophobic core of both neutral and acidic phospholipids. Finally, our data suggest that palmitoylation of previously myristoylated sequences could be responsible of the partition into lipids rafts observed for this type of acylated proteins.