INTERACTION OF WILD-TYPE SIGNAL SEQUENCES AND THEIR CHARGED VARIANTS WITH MODEL AND NATURAL MEMBRANES

The interaction of synthetic peptides corresponding to wild-type signa l sequences, and their mutants having charged amino acids in the hydro phobic region, with model and natural membranes has been studied. At h igh peptide concentrations, i.e. low lipid/peptide ratios, the signal peptides cause release of carboxy-fluorescein (CF) from model membrane s with lipid compositions corresponding to those of translocation-comp etent as well as translocation-incompetent membranes. Interestingly, m utant sequences, which were non-functional in vivo, caused considerabl e release of CF compared with the wild-type sequences. Both wild-type and mutant signal sequences perturb model membranes even at lipid/pept ide ratios of 1000:1, as indicated by the activities of phospholipases A2, C and D. These studies indicate that such mutant signals are non- functional not because of their inability to interact with membranes, but due to defective targeting to the membrane. The signal peptides in hibit phospholipase C activity in microsomes, uncouple oxidative phosp horylation in mitochondria and increase K+ efflux from erythrocytes, a nd one of the mutant sequences is a potent degranulator of the mast ce lls. Both wild-type and mutant signal sequences have the ability to pe rturb vesicles of various lipid compositions. With respect to natural membranes, the peptides do not show any bias towards translocation-com petent membranes.