Molecular Conformation and Topography of a Synaptic Lipo-Peptide in Simulated Synaptosomal Membrane Lipids

Abstract

Synaptosomal proteins have a number of vicinal cysteine and lysine residue side chains that may be covalently palmitoylated via ester or acyl linkages. Synthesis of a twenty-one residue peptide derived from the synaptosomal protein Synaptotagmin (sequence residues 72 - 92) using Fmoc chemistry with Cysteine carrying side-chain thioether linked palmitate was used to characterize the structure and activity of the lipo-peptide with multilayer phospholipid vesicles having POPC and POPS composition representative of synaptosomal membranes. The peptide dissolved freely in chloroform, methanol, 1% formic acid in water (4/4/1; v/v) and its primary structure was analyzed by high-resolution electrospray-ionization mass spectrometry confirming accurate synthesis. Both collisionally activated and electron-capture dissociation (CAD/ECD) techniques provided complementary information on fatty acylation sites. Secondary structure analysis of the peptide after reconstitution in multilayer vesicles using FTIR - ATR spectroscopy indicated that the dominant conformation of the peptide in this environment was extended beta sheet. We hypothesize that the membrane-associated fatty beta motif modulates vesicle-membrane fusion interactions.