Raft-targeting and oligomerization of Parasporin-2, a bacillus thuringiensis crystal protein with anti-tumour activity

J Biochem. 2008 Feb;143(2):269-75. doi: 10.1093/jb/mvm220. Epub 2007 Nov 15.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Biopolymers
  • Drug Screening Assays, Antitumor
  • Endotoxins / chemistry*
  • Endotoxins / metabolism
  • Endotoxins / pharmacology*
  • Subcellular Fractions / metabolism


  • Biopolymers
  • Endotoxins
  • parasporin-2, Bacillus thuringiensis