Transient vesicle leakage initiated by a synthetic apoptotic peptide derived from the death domain of neurotrophin receptor, p75NTR.

Peptides that induce apoptosis have potential as anticancer therapeutics. The design of safe, effective cancer therapeutic peptides requires characterization of the physical and chemical properties that influence activation of cell death in neoplastic cells. NTR365 is a synthetic pro-apoptotic peptide with an amino acid sequence derived from the death domain of p75(NTR). These studies were initiated to identify a potential mechanism for the apoptotic activity of NTR365 identified by Rabizadeh et al. We examined the interactions of this synthetic pro-apoptotic peptide with phospholipid vesicles. Fluorescence experiments demonstrate that the peptide induces leakage from large unilamellar vesicles. Leakage activity is transient and dependent on the presence of anionic lipid in the vesicles. Circular dichroism studies show that the NTR365 adopts a different conformation and may have altered vesicle affinity under conditions conducive to leakage. The active conformation of NTR365 differs from that of the NMR derived conformation. A related peptide with a single substitution is not apoptotically active, does not form a helical structure in the presence of vesicles and does not induce appreciable vesicle leakage under the same conditions as NTR365. These studies suggest that the demonstrated apoptotic activity of a closely related NTR364 peptide is linked to disruption of a membrane barrier and to the ability of the peptide to form a helical structure.