Defining the interaction of perforin with calcium and the phospholipid membrane

Following its secretion from cytotoxic lymphocytes into the immune synapse, perforin binds to target cell membranes through its Ca2 + -dependent C2 domain. Membrane-bound perforin then forms pores that allow passage of pro-apoptopic granzymes into the target cell. In the present study, structural and biochemical studiesrevealthatCa2+ bindingtriggersaconformationalchange in the C2 domain that permits four key hydrophobic residues to interact with the plasma membrane. However, in contrast with previous suggestions, these movements and membrane binding do not trigger irreversible conformational changes in the pore-forming MACPF (membrane attack complex/perforin- like) domain, indicating that subsequent monomer–monomer interactions at the membrane surface are required for perforin pore formation.

穿孔素（perforin）从细胞毒性淋巴细胞（cytotoxic lymphocytes）分泌至免疫突触（immune synapse）后，通过其依赖Ca²⁺的C2结构域（C2 domain）与靶细胞膜结合。膜结合的穿孔素随后形成孔道，允许促凋亡颗粒酶（pro-apoptopic granzymes）进入靶细胞。本研究中，结构与生化分析表明，Ca²⁺结合会触发C2结构域的构象变化（conformational change），使四个关键疏水残基（hydrophobic residues）能够与质膜（plasma membrane）相互作用。然而，与先前的推测相反，这些构象运动及膜结合并不会触发成孔MACPF（膜攻击复合物/穿孔素样，membrane attack complex/perforin-like）结构域的不可逆构象变化，这表明穿孔素孔道的形成需要膜表面后续的单体-单体相互作用（monomer–monomer interactions）。