FLUORESCENCE STUDIES ON THE INTERACTION OF A SYNTHETIC SIGNAL PEPTIDEAND ITS ANALOG WITH LIPOSOMES

The N-terminal signal sequence of glucitol permease of Escherichia col i (Gut22: MIETITHGAEWFIGLFQKGGEC) and its analog (Gut22Ana: MIETITPGAV WFIGLFQKGGEC) were synthesized. The analog had a Pro residue substitut ed for the His at the 7th position of Gut22 and a Val residue substitu ted for the Glu at the 10th position. Previous studies indicated that due to its structural rigidity, the interaction of Gut22Ana with lipid bilayer was much weaker than that of Gut22 (Wang, Q.D., Cui, D.F. and Lin, Q.S. (1996) Science in China (Series C) 39, 395-405). To further probe the location of the tryptophan residues of the peptides in lipi d bilayer, the membrane penetration depth of the tryptophan residue of Gut22 was measured using spin-labeled phospholipids, and fluorescence quenching of the peptides by iodide and acrylamide in the presence an d absence of phosphatidylserine/phosphatidylcholine liposomes were als o studied. Fluorescent labeling of the peptides enabled the study of t heir association with membrane by fluorospectrophotometry. In the pres ence of liposomes, the peptides were protected from reaction with chym otrypsin, indicating that the peptide incorporated into the membrane. However, dithionite, which acts external to the membrane, reacted with the peptide, showing that the peptides did not translocate across lip id bilayer spontaneously.