BBB Seminar: Gregor Anderluh
Perforin adventures on lipid membranes
Laboratory for Molecular Biology and Nanobiotechnology, National Institute of Chemistry, Ljubljana, and Infrastructural Centre for Molecular Interactions Analysis, Department of Biology, University of Ljubljana, Slovenia
Perforin is important for proper functioning of the immune system. It is released from cytotoxic cells upon recognition of virus-infected or tumorigenic cells. It also has a major role in graft-vs-host disease in allogenic stem cell and bone marrow transplantations. Perforin forms pores in the membranes of target cells. Somehow it allows granzymes, proteolytic enzymes that are present in cytolytic granules and co-released with perforin, to enter the cells and initiate programmed cell death. In this way dangerous cells are eliminated without any damage to nearby tissues and organs. It is not yet satisfactorily explained how perforin enables the entry of other molecules into cells and currently two models that describe this process exist. Furthermore, its mechanism of action at the molecular level is not yet completely understood.
Perforin belongs to the MACPF/CDC protein superfamily, characterised by the protein domain that, upon protein association with the lipid membrane, allows formation of a transmembrane pore. Many efforts are currently being invested to understand the perforin mechanism of membrane damage. We have investigated how native human perforin forms pores in membranes, which factors affect pore formation and determine the dimensions of its pores. Pores formed in planar lipid bilayers are heterogeneous. Overall, we have identified three types of events: the formation of small and large pores and frequent membrane breakages. By using cryo-EM we monitored the pre-pore intermediate that was found to sit atop an unperturbed membrane. When studying pores in model lipid systems, such as giant unilamellar vesicles, we surprisingly also discovered that perforin is capable of remodelling the lipid membrane to induce invaginations and formation of secondary vesicles, which have engulfed the surrounding medium. Perforin thus exhibits different activities and is capable of inducing an endocytosis-like event in addition to pore formation, which may be physiologically relevant for granzyme delivery in vivo.
Anderluh G and Lakey JH (2008) Disparate proteins use similar architectures to damage membranes. Trends Biochem. Sci. 33: 482-490.
Praper T et al. (2010) Human perforin permeabilizing activity, but not binding to lipid membranes, is affected by pH. Mol. Immunol. 47: 2492-2504.
Praper T et al. (2011) Human perforin employs different avenues to damage membranes. J. Biol. Chem. 286: 2946-2955.
Praper T et al. (2011) Perforin activity at membranes leads to invaginations and vesicle formation. Proc. Natl. Acad. Sci. USA. 108: 21016-21021.
Chair: Øyvind Halskau, Department of Molecular Biology