Synthesis and characterization of a chimeric peptide derived from fasciculin that inhibits acetylcholinesterase.

Fasciculins are peptides isolated from mamba (Dendroaspis) venoms which exert their toxic action by inhibiting acetylcholinesterase (AChE). They contain a characteristic triple stranded antiparallel beta-sheet formed by residues 22-27, 34-39 and 48-53. A chimeric peptide named Fas-C, encompassing most of these sequences was synthesized using SPPS/Boc-chemistry and characterized chemically, structurally and functionally. Fas-C has two disulfide bridges, formed sequentially using dual cysteine protection. SDS-PAGE patterns, HPLC profiles and MS proved the peptide identity. Circular dichroism indicated the presence of 13.6% and 41.6% of beta-sheet and beta-turn, respectively, comparable to values observed in the native toxin. An inhibitory effect on eel AChE was displayed by the peptide (Ki71.6 +/- 18.3 microM), although not reaching the affinity level of the parent native toxin (Ki 0.3 nM). It is confirmed that the principal binding region of fasciculin to AChE resides within loop II.