INFLUENCE OF A NH2-TERMNINAL EXTENSION ON THE ACTIVITY OF KTX2, A K-AUSTRALIS SCORPION-VENOM( CHANNEL BLOCKER PURIFIED FROM ANDROCTONUS)

A cDNA encoding a short polypeptide blocker of K+ channels, kaliotoxin 2 (KTX2), from the venom of the North African scorpion Androctonus au stralis was expressed in the periplasmic space of Escherichia coli. KT X2 was produced as a fusion protein with the maltose binding protein f ollowed by the recognition site for factor Xa or enterokinase precedin g the first amino acid residue of the toxin. The fully refolded recomb inant KTX2 (rKTX2) was obtained (0.15-0.30 mg/l of culture) and was in distinguishable from the native toxin according to chemical and biolog ical criteria. An N-extended analogue of KTX2 exhibiting three additio nal residues was also expressed. This analogue had 1000-fold less affi nity for the I-125-kaliotoxin binding site on rat brain synaptosomes t han KTX2. Conformational models of KTX2 and its mutant were designed b y amino acid replacement using the structure of agitoxin 2 from Leiuru s quinquestriatus as template, to try to understand the decrease in af finity for the receptor. (C) 1997 Federation of European Biochemical S ocieties.