Title:The Sensing of Membrane Microdomains Based on Pore-Forming Toxins
VOLUME: 20 ISSUE: 4
Author(s):M. Skocaj, B. Bakrac, I. Krizaj, P. Macek, G. Anderluh and K. Sepcic
Affiliation:Department of Biology, Biotechnical Faculty, University of Ljubljana, Vecna pot 111, 1000 Ljubljana, Slovenia.
Keywords:Cholesterol, equinatoxin, fluorescent probe, liquid ordered phase, lysenin, membrane microdomains, membrane raft, ostreolysin, perfringolysin O, sphingomyelin
Abstract:Membrane rafts are transient and unstable membrane microdomains that are enriched in sphingolipids, cholesterol, and specific
proteins. They are involved in intracellular trafficking, signal transduction, pathogen entry, and attachment of various ligands. Increasing
experimental evidence on the crucial biological roles of membrane rafts under normal and pathological conditions require new
techniques for their structural and functional characterization. In particular, fluorescence-labeled cytolytic proteins that interact specifically
with molecules enriched in rafts are of increasing interest. Cholera toxin subunit B interacts specifically with raft-residing ganglioside
GM1, and it has long been the lipid probe of choice for membrane rafts. Recently, four new pore-forming toxins have been proposed
as selective raft markers: (i) equinatoxin II, a cytolysin from the sea anemone Actinia equina, which specifically recognizes free and
membrane-embedded sphingomyelin; (ii) a truncated non-toxic mutant of a cytolytic protein, lysenin, from the earthworm Eisenia
foetida, which specifically recognizes sphingomyelin-enriched membrane domains; (iii) a non-toxic derivative of the cholesteroldependent
cytolysin perfringolysin O, from the bacterium Clostridium perfringens, which selectively binds to membrane domains enriched
in cholesterol; and (iv) ostreolysin, from the mushroom Pleurotus ostreatus, which does not bind to a single raft-enriched lipid
component, but requires a specific combination of two of the most important raft-residing lipids: sphingomyelin and cholesterol. Nontoxic,
raft-binding derivatives of cytolytic proteins have already been successfully used to explore both the structure and function of
membrane rafts, and of raft-associated molecules. Here, we review these four new derivatives of pore-forming toxins as new putative
markers of these membrane microdomains.
