Lysenin

Lysenin is a protein toxin produced by the earthworm Eisenia fetida. It belongs to the aerolysin-like pore-forming toxin family. Lysenin is notable for its ability to specifically bind to sphingomyelin, a lipid found in eukaryotic cell membranes, particularly in lipid rafts. This binding is crucial to its mechanism of action.

Upon binding to sphingomyelin, lysenin oligomerizes, assembling into ring-shaped structures that insert into the cell membrane. These oligomeric structures form pores, disrupting the membrane's integrity and leading to cellular leakage and ultimately, cell death. The pore size created by lysenin is estimated to be large enough to allow the passage of relatively large molecules.

Lysenin's specificity for sphingomyelin has made it a valuable tool in cell biology research. It is used to study the distribution and function of sphingomyelin in cell membranes, and to investigate the role of lipid rafts in various cellular processes, such as signal transduction and membrane trafficking. Furthermore, lysenin has been investigated for its potential applications in drug delivery, where it could be used to create pores in cells to facilitate the entry of therapeutic agents.

Lysenin is typically isolated from earthworm tissues. While it is a toxin, its effects are primarily observed in vitro or through localized application in vivo. Its systemic toxicity is relatively low due to its limited ability to cross biological barriers.