Pore Formation by Pore Forming Proteins in Lipid Membranes: Structural Insights Through Cryo-EM

Many pathogenic bacteria utilize their complicated appalling arsenal, bacterial virulence factors, to attack host cells by damaging the host cell membrane and neutralizing host defense mechanisms. Bacterial pore-forming proteins (PFPs) are one of them, they include a distinct class of secreted soluble toxin monomers, which binds to the specific cell surface receptors and /or lipids, oligomerizes as an amphipathic transmembrane pore complex on host cell membranes, and deforms the integrity of the plasma membrane. Researchers have focused on characterizing the structure and function of different Pore Forming Toxins (PFTs) from various organisms, where most of the structural studies employed X-ray crystallography, single-particle cryo-EM, and cryo-electron tomography. However, historically, most of these previous studies focused on using detergent to solubilize and oligomerize the PFTs. Additionally, previous studies have also shown that lipid membranes and lipid components, including cell surface receptors, play a critical role in pore formation and oligomerization. However, there are limited studies available that aim to resolve the structure and function of PFTs in liposomes. In this review article, we majorly focused on structural and functional studies of pore-forming toxins in the presence of detergents, lipid nanodiscs, and liposomes. We will also discuss the challenges and benefits of using liposomes to study pore-forming proteins in more biologically relevant membrane environments.