Title : The structural basis for membrane binding and pore formation by lymphocyte
perforin
Abstract :
- Natural killer cells and cytotoxic T lymphocytes accomplish the critically important function of killing virus-infected and neoplastic cells
- They do this by releasing the pore-forming protein perforin and granzyme proteases from cytoplasmic granules into the cleft formed between the abutting killer and target cell membranes
- Perforin , a 67-kilodalton multidomain protein , oligomerizes to form pores that deliver the pro-apoptopic granzymes into the cytosol of the target cell
- The importance of perforin is highlighted by the fatal consequences of congenital perforin deficiency, with more than 50 different perforin mutations linked to familial haemophagocytic lymphohistiocytosis (type 2 FHL)
- Here we elucidate the mechanism of perforin pore formation by determining the X-ray crystal structure of monomeric murine perforin , together with a cryo-electron microscopy reconstruction of the entire perforin pore
- Perforin is a thin 'key-shaped' molecule, comprising an amino-terminal membrane attack complex perforin-like (MACPF)/cholesterol dependent cytolysin (CDC) domain followed by an epidermal growth factor ( EGF ) domain that, together with the extreme carboxy-terminal sequence , forms a central shelf-like structure
- A C-terminal C2 domain mediates initial, Ca(2 +)-dependent membrane binding
- Most unexpectedly, however, electron microscopy reveals that the orientation of the perforin MACPF domain in the pore is inside-out relative to the subunit arrangement in CDCs
- These data reveal remarkable flexibility in the mechanism of action of the conserved MACPF/CDC fold and provide new insights into how related immune defence molecules such as complement proteins assemble into pores