Raft-targeting and oligomerization of Parasporin-2, a bacillus thuringiensis crystal protein with anti-tumour activity.
Parasporin-2 is a newly classified Bacillus thuringiensis crystal toxin with strong cytocidal activities toward human liver and colon cancer cells. Similar to other insecticidal B. thuringiensis crystal toxins, parasporin-2 shows target specificity and damages the cellular membrane. However, the mode of parasporin-2 actions toward the cell membrane remains unknown. Here, we show that this anti-tumour crystal toxin targets lipid rafts and assembles into oligomeric complexes in the membrane of human hepatocyte cancer (HepG2) cells. Upon incubation with HepG2 cells, peripheral membrane-bound toxins, which were recovered in a low-density detergent-resistant membrane fraction, i.e. with lipid rafts, were transformed into heat-stable SDS-resistant membrane-embedded oligomers (approximately 200 kDa). The toxin oligomerization was dependent on temperature and coupled with cell lysis. The toxin oligomerization also occurred in a cell-free membrane system and was required for binding to membrane proteins, the lipid bilayer and cholesterols. These results indicate that parasporin-2 is an oligomerizing and pore-forming toxin that accumulates in lipid rafts.
Abe
Yuichi
Y
Department of Chemistry, Faculty of Sciences, Kyushu University, Fukuoka 812-8581, Japan.
Shimada
Hiroyasu
H
Kitada
Sakae
S
D001704:Biopolymers; D004354:Drug Screening Assays, Antitumor; D004731:Endotoxins / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology*; D013347:Subcellular Fractions / Q000378:metabolism
D001704:Biopolymers; D004731:Endotoxins; C515506:parasporin-2, Bacillus thuringiensis