Effect of two polyamine toxins on the bacterial porin OmpF

Spermine, a polyamine based on a 12-carbon motif, is an effective inhibitor off. coli OmpF porin, Here we study the inhibition of porin by two polyamine toxins commonly used as modulators of polyamine-sensitive channels: Philanthotoxin-433 (PhTX) from wasp venom and Joro spider toxin (JSTX). Both are highly asymmetric molecules, with at one end a la-carbon chain polyamine targeting the molecule to the porin constriction zone, and at the other end large aromatic groups conferring to this extremity a size in the order of the OmpF constriction zone, Here we report that PhTX, but not Joro toxin, induces a high degree of bickering in the OmpF-mediated current. The effect is concentration and voltage-dependent, and greatly diminished in a mutant lacking D113 on the constriction loop, a residue previously shown to be required for spermine sensitivity. Possible reasons for the distinct sensitivity of OmpF to PhTX and Joro toxin are discussed. (C) 2001 Academic Press.