Structure and mechanism of bactericidal mammalian perforin-2, an ancient agent of innate immunity
Tao Ni, Fang Jiao, Xiulian Yu, Saša Aden, Lucy Ginger, Sophie I. Williams, Fangfang Bai, Vojtěch Pražák, Dimple Karia, Phillip J. Stansfeld, Peijun Zhang, George P. Munson, Gregor Anderluh, Simon Scheuring, Robert J.C. Gilbert
Abstract
Perforin-2 (MPEG1) is thought to enable the killing of invading microbes engulfed by macrophages and other phagocytes, forming pores in their membranes. Loss of perforin-2 renders individual phagocytes and whole organisms significantly more susceptible to bacterial pathogens. Here, we reveal the mechanism of perforin-2 activation and activity using atomic structures of pre-pore and pore assemblies, high-speed atomic force microscopy, and functional assays. Perforin-2 forms a pre-pore assembly in which its pore-forming domain points in the opposite direction to its membrane-targeting domain. Acidification then triggers pore formation, via a 180° conformational change. This novel and unexpected mechanism prevents premature bactericidal attack and may have played a key role in the evolution of all perforin family proteins.