Design and synthesis of peptides that bind alpha-bungarotoxin with high affinity

Background: alpha -Bungarotoxin (alpha -BTX) is a highly toxic snake venom alpha -neurotoxin that binds to acetylcholine receptor (AChR) at the neurom uscular junction, and is a potent inhibitor of this receptor. We describe t he design and synthesis of peptides that bind alpha -BTX with high affinity , and inhibit its interaction with AChR with an IC50 of 2 nM. The design of these peptides was based on a lead peptide with an IC50 Of 3 x 10(-7) M, p reviously identified by us [M. Balass et al., Proc. Natl. Acad. Sci. USA 94 (1997) 6054] using a phage-display peptide library. Results: Employing nuclear magnetic resonance-derived structural informatio n [T. Scherf et al., Proc. Natl. Acad. Sci. USA 94 (1997) 6059] of the comp lex of (alpha -BTX with the lead peptide, as well as structure-function ana lysis of the ligand-binding site of AChR, a systematic residue replacement of the lead peptide, one position at a time, yielded 45 different 13-mer pe ptides. Of these, two peptides exhibited a one order of magnitude increase in inhibitory potency in comparison to the lead peptide. The design of addi tional peptides, with two or three replacements, resulted in peptides that exhibited a further increase in inhibitory potency (IC50 values of 2 nM), t hat is more than two orders of magnitude better than that of the original l ead peptide, and better than that of any known peptide derived from AChR se quence. The high affinity peptides had a protective effect on mice against (alpha -BTX lethality. Conclusions: Synthetic peptides with high affinity to (alpha -BTX may be us ed as potential lead compounds for developing effective antidotes against a lpha -BTX poisoning. Moreover, the procedure employed in this study may ser ve as a general approach for the design and synthesis of peptides that inte ract with high affinity with any desired biological target. (C) 2001 Elsevi er Science Ltd. All rights reserved.