The Amino Acid Region 115–119 of Ammodytoxins Plays an Important Role in Neurotoxicity

Phenylalanine-24 in the N-terminal region of ammodytoxins is important for both enzymic activity and presynaptic toxicity

“…Nevertheless, our results indicate clearly that, in addition to certain C-terminal aromatic and hydrophobic residues [17,18], the N-terminal aromatic residue Phe#%, on the IBS is involved in the neurotoxicity of AtxA.…”

“…It has been shown that Phe"#%, which is replaced by isoleucine in AtxC, is responsible for the higher toxicity of AtxA [18]. Furthermore, an AtxA mutant in which Tyr""& and Ile""' were replaced by lysines showed a 240-fold decrease in toxicity [17]. In addition, a six-site charge-Phe 24 influences ammodytoxin toxicity and enzymic activity…”

“…Three Atx-binding proteins, R25 [14], R180 [15] and calmodulin [16], have been identified recently in porcine cerebral cortex, and may have a potential role in presynaptic toxicity. Our previous studies have indicated that certain aromatic residues in the C-terminal part of AtxA are important for toxicity [17,18]. In the present study, we have investigated the possible involvement of another surfaceexposed aromatic residue (Phe#%), located in the N-terminal part but in the vicinity of those C-terminal residues.…”

Protein Engineering in Structure-Function Studies of Viper's Venom Secreted Phospholipases A2

“…First, we introduced the N-terminal half of AtxA into DPLA 2 by preparing the chimeric AtxA/DPLA 2 protein. Its lethal potency was relatively low, in the range of those of DPLA 2 and the AtxA KKML mutant (Table 1 and Ivanovski et al, 2000), confirming that it is primarily the presence of the KKML cluster in the C-terminus of the chimera that has a strong negative influence on toxicity. Secondly, by substituting the KKML cluster in DPLA 2 with the YIRN cluster of AtxA, we produced a chimeric mutant (AtxA/DPLA 2 YIRN ) that is 58-fold higher in lethal potency than is AtxA/DPLA 2 , reaching a level of toxicity similar to that of the highly neurotoxic AtxA.…”

“…According to our earlier structure-function analyses, the more than one order of magnitude lower toxicity of AtxC than that of AtxA is a consequence of the substitution of the aromatic Phe124 by Ile (Pungerčar et al, 1999). Furthermore, in accordance with the three substitutions responsible for the difference in toxicities of AtxA and AtxB, several other C-terminal residues of AtxA, namely the Tyr115/Ile116/ Arg118/Asn119 (YIRN) cluster, were shown to be important for the neurotoxicity of Atxs (Ivanovski et al, 2000). Thus, the lethal potency of the AtxA-Y115K/I116K/R118M/N119L (AtxA KKML ) mutant was 290-fold lower than that of AtxA (Ivanovski et al, 2000 and The KKML cluster is present in the weakly neurotoxic DPLA 2 from the venom of Russell's viper, Daboia (Vipera) russelii russelii, which shares a high level of amino acid identity (82%) with AtxA.…”