Low density lipoprotein inactivates Vibrio vulnificus cytolysin through the oligomerization of toxin monomer

Blood lipoprotein has been shown to be an important defense factor against the bacterial infection. Lipoprotein is scavenger of bacterial endotoxin (lipopolysaccharide, LPS). However, there is little evidence showing its protective action against the bacterial exotoxin. We have previously demonstrated that cholesterol inactivates Vibrio vulnificus cytolysin (VVC) through oligomerization of the toxin monomer. The aim of the present study was to investigate the relationship between VVC and low-density lipoprotein cholesterol (LDL-C). LDL induced the oligomerization of VVC in a dose-dependent manner. The oligomerization of VVC monomer with LDL was demonstrated by immunoblotting, which exhibited 200-kDa bands corresponding to a tetramer of the native VVC of relative molecular weight of 51,000. Moreover, LDL inactivated hemolytic activity of VVC in a dose-dependent manner, and this response was not changed by the modifications of LDL (heat denaturation of proteins and peroxidation of phospholipids), suggesting that LDL-C is associated with the defense action against VVC. These results suggest that LDL-C inactivates VVC through the induction of toxin oligomerization.