SOLUTION STRUCTURE OF A SYNTHETIC LYTIC PEPTIDE - THE PERFORIN AMINO-TERMINUS

Background: Killer lymphocytes secrete perforin, a 67 kDa protein that initiates T-cell cytolysis following aggregation and pore formation i n target membranes. The resulting pores cause a breakdown of the trans membrane osmotic gradient and allow other cytolytic mediators to enter the target cell and initiate apoptosis, The cytolytic domain resides within the first 34 residues of the amino terminus of perforin, with r esidues 1-19 being sufficient for cytolytic activity. Results: The sol ution structure of a 22-residue synthetic peptide (P-22), correspondin g to the amino terminus of human perforin, has been determined using h igh resolution nuclear magnetic resonance spectroscopy in the presence and absence of perdeuterated detergent (SDS) micelles. In aqueous sol ution, P-22 exists mainly in a random conformation. However, it adopts a hooklike structure at the carboxyl terminus in the presence of SDS micelles when the positively charged residues cluster to form a turn t hat provides a binding surface to the negatively charged sulfate headg roups. Conclusions: The strong electrostatic interaction between the c ationic region of the P-22 peptide and the lipid headgroups probably w eakens the membrane, facilitating insertion of the relatively neutral/ hydrophobic stretch of P-22, and is representative of the initial step of the lytic pathway. The structural model described here is probably relevant to understanding the mechanisms of other cationic antimicrob ial peptides.