Channel formation and [Ca²⁺](i) accumulation induced by perforin N-terminus peptides: Comparison with purified perforin and whole lytic granules

Cytotoxic T lymphocytes (CTL) and natural killer (NK) cells express the pore forming protein perforin, which contributes to lymphocytotoxicity. The hallmark of perforin action is opening high-conductance transmembrane channels that enable massive influx of Ca²⁺ ions (deleterious to many cell types), as well as granzymes, which may trigger the apoptotic pathway. To explore the functional domains in the perforin molecule, we investigated in PN71 lymphocytes, the ability of perforin N-terminus synthetic peptides (compared to purified perforin and perforin-containing lytic granules), to cause intracellular Ca²⁺ ([Ca²⁺](i)) accumulation and open transmembrane channels. To this end, we used the whole cell recording technique and Indo 1 fluorescence to measure membrane currents and [Ca²⁺](i), respectively. We have demonstrated that the N-terminus peptide Hu-34 (amino acids 1-34) closely resembled perforin action, reflected by [Ca²⁺](i) accumulation and channel activity, while shorter peptides (e,g., Hu-16) generated mostly short-lived channels but no [Ca²⁺](i) elevation. Hence, the first 34 amino acids of the perforin N-terminus sequence are sufficient for the perforin action.