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The MACPF protein superfamily is named after a domain that is common to the membrane attack complex (MAC) proteins of complement (C6, C7, C8α, C8β and C9) and perforin (PF). Many members of this protein family are important pore forming toxins in eukaryotes. The archetypal members of the family are complement C9 and perforin, both of which function in human immunity. C9 functions by punching holes in the membranes of Gram-negative bacteria. Perforin is released by cytotoxic T cells and lyses virally infected and transformed cells. In addition perforin permits delivery of cytotoxic proteases called granzymes that cause cell death. Deficiency of either protein can result in human disease. Structural studies reveal that MACPF domains are related to cholesterol dependent cytolysins (CDCs), a family of pore forming toxins previously thought to only exist in bacteria.〔 ==Biological roles of MACPF domain containing proteins== To date, around 500 members of the MACPF superfamily have been identified. Many of these proteins play key roles in the plant and animal immunity. The complement proteins C6-C9 all contain a MACPF domain and assemble into the membrane attack complex. C6, C7 and C8β appear to be non-lytic and function as scaffold proteins within the MAC. In contrast both C8α and C9 are capable of lysing cells. The final stage of MAC formation involves polymerisation of C9 into a large pore that punches a hole in the outer membrane of Gram negative bacteria. Perforin is stored in granules within cytotoxic T-cells and is responsible for killing virally infected and transformed cells. Perforin functions via two distinct mechanisms. Firstly, like C9, high concentrations of perforin can form pores that lyse cells. Secondly, perforin permits delivery of the cytotoxic granzymes A and B into target cells. Once delivered, granzymes are able to induce apoptosis and cause target cell death.〔 The plant protein CAD1 functions in the plant immune response to bacterial infection. The sea anemone ''Actineria villosa'' uses a MACPF protein as a lethal toxin. MACPF proteins are also important for the invasion of the Malarial parasite into the mosquito host and the liver. Not all MACPF proteins function in defence or attack. For example, astrotactin is involved in neural cell migration in mammals and apextrin is involved in sea urchin (''Heliocidaris erythrogramma'') development. ''Drosophila'' Torso-like protein, which controls embryonic patterning, also contains a MACPF domain.〔 It is unknown whether the function of any of these proteins involves lytic activity. Functionally uncharacterised MACPF proteins are sporadically distributed in bacteria. Several species of ''Chlamydia'' contain MACPF proteins. The insect pathogenic bacteria ''Photorhabdus luminescens'' also contains a MACPF protein, however, this molecule appears non-lytic.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「MACPF」の詳細全文を読む スポンサード リンク
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