Biophysical Studies of Peptides that Translocate through Cell Membranes: Induced Structures and Membrane Interactions

Abstract

Biophysical techniques such as high resolution NMR, CD, linear dichroism and fluorescence spectroscopy have been used to investigate the interactions of cell penetrating peptides (CPPs) with various membrane mimetic solvent systems. A pH gradient appears to be required to drive the peptide across a unilamellar phospholipid vesicle bilayer. Membrane leakage induction by CPPs (possibly associated with transient pore formation) in unilamellar vesicles has been studied in parallel with peptide translocation. The membrane perturbation caused by the TP10 peptide depends on the type and size of cargo attached to the peptide, and the potent leakage caused by the peptide alone is lost when the peptide is attached to a large cargo. Effects of the hydrophobic negatively charged counter-ion pyrene butyrate on membrane leakage has been studied for selected CPPs and compared to its CPP-enhancing efficiency using biological assays. The different proposed mechanisms for CPP activities will be discussed based on these observations.We have also studied native peptide sequences which have CPP activities that may be related to a biological function. These are peptides derived from the N-terminal sequence of prion proteins (including the signal sequence) from mouse or cow. The prion protein derived peptides have shown an unexpected activity in counteracting scrapie infections in a neuronal cell system. We hypothesize that the CPP activity of the peptides may guide them into a specific cellular compartment where they may interfere with the prion protein aggregation and structure conversion into the scrapie form.