The role of tryptophan residues in the hemolytic activity of stonustoxin, a lethal factor from stonefish (Synanceja horrida) venom

Stonustoxin (SNTX) is a pore-forming cytolytic lethal factor, isolated from the venom of the stonefish Synanceja horrida, that has potent hemolytic ac tivity. The role of tryptophan residues in the hemolytic activity of SNTX w as investigated. Oxidation of tryptophan residues of SNTX with N-bromosucci nimide (NBS) resulted in loss of hemolytic activity. Binding of 8-anilino-1 -naphthalenesulphonate (ANS) to SNTX resulted in occlusion of tryptophan re sidues that resulted in loss of hemolytic activity. Circular dichroism and fluorescence studies indicated that ANS binding resulted in a conformationa l change of SNTX, in particular, a relocation of surface tryptophan residue s to the hydrophobic interior. NBS-modification resulted in oxidised surfac e tryptophan residues that did not relocate to the hydrophobic interior. Th ese results suggest that native surface tryptophan residues play a pivotal role in the hemolytic activity of STNX, possibly by being an essential comp onent of a hydrophobic surface necessary for pore-formation. This study is the first report on the essentiality of tryptophan residues in the activity of a lyric and lethal factor from a fish venom. (C) 2000 Societe francaise de biochimie et biologie moleculaire / Editions scientifiques et medicales Elsevier SAS.