Design, synthesis and structure of an amphipathic peptide with pH-inducible haemolytic activity

A synthetic, 26–residue peptide having a strong helixforming potential in the protonated state was designed to interactwith lipid bilayers in a pH–dependent way. On the basisof this concept a cluster of four glutamk acid residues wasinserted in the central region of the amphipathic peptide topromote helix destabilization by mutual charge repulsion atneutral pH. Protonation of these residues might then bring aboutboth a pH-mediated change in hydrophobteity and conformationforming a membrane–active amphiphilk helix. The sequenceGLGTLLTLLEFLLEELLEFLKRKRQQamide produced by the design strategyinduced pH–triggered lysis of human erythrocytes. A molecularmodel correlating the lytic activity to the formation of transmembranepores which were detected by electron microscopy in erythrocytemembranes is discussed. Circular dichroism studies indicateda selfassociation of the monomeric random coil form with increasingpeptide concentration leading to the apparent induction of stronga-helix formation ({small tilde} 100% helkity) in the fullyaggregated state. However, no pH–dependent helixrandomcoil transition was observed, implying that interhelical hydrophobkand ionic interactions not only govern the self–associationbut also decisively influence the conformational stability ofthe peptide.