Deciphering the Molecular Mechanism and Function of Pore-Forming Toxins using Leishmania major.

Understanding the function and mechanism of pore-forming toxins (PFTs) is challenging because cells resist the membrane damage caused by PFTs. While biophysical approaches help understand pore formation, they often rely on reductionist approaches lacking the full complement of membrane lipids and proteins. Cultured human cells provide an alternative system, but their complexity and redundancies in repair mechanisms make identifying specific mechanisms difficult. In contrast, the human protozoan pathogen responsible for cutaneous leishmaniasis, Leishmania major, offers an optimal balance between complexity and physiologic relevance. L. major is genetically tractable and can be cultured to high density in vitro, and any impact of perturbations on infection can be measured in established murine models. In addition, L. major synthesizes lipids distinct from their mammalian counterparts, which could alter membrane dynamics. These alterations in membrane dynamics can be probed with PFTs from the best-characterized toxin family, cholesterol-dependent cytolysins (CDCs). CDCs bind to ergosterol in the Leishmania membrane and can kill L. major promastigotes, indicating that L. major is a suitable model system for determining the cellular and molecular mechanisms of PFT function. This work describes methods for testing PFT function in L. major promastigotes, including parasite culture, genetic tools for assessing lipid susceptibility, membrane binding assays, and cell death assays. These assays will enable the rapid use of L. major as a powerful model system for understanding PFT function across a range of evolutionarily diverse organisms and commonalities in lipid organization.