Pore-forming protein that plays a key role in granzyme-mediated programmed cell death, and in defense against virus-infected or neoplastic cells. Plays an important role in killing other cells that are recognized as non-self by the immune system, e.g. in transplant rejection or some forms of autoimmune disease. Can insert into the membrane of target cells in its calcium-bound form, oligomerize and form large pores. Promotes cytolysis and apoptosis of target cells by mediating the passage and uptake of cytotoxic granzymes. Facilitates the delivery of cationic cargo protein, while anionic or neural proteins are not delivered efficiently. Perforin pores allow the release of mature caspase-7 (CASP7) into the extracellular milieu.