Structural Determinants of Fasciculin Specificity for Acetylcholinesterase

Abstract

Fasciculins are the only known peptide inhibitors of acetylcholinesterase (AChE) with a high degree of selectivity. They are found in mamba snake venoms and have been shown to display powerful inhibitory activity toward mammalian and fish AChE. To date, four iso-fasciculins have been characterized: fasciculin 1 (FASI) and fasciculin 2 (FAS2) from the venom of Dendroaspis angusticeps (Rodriguez-Ithurralde et al., 1983), toxin C from the venom of D. polylepis (Joubert and Taljaard, 1978), and fasciculin 3 (FAS3) from a venom of D. viridis (Marchot et al., 1993). The early pharmacological and biochemical studies of FAS2, carried out both in vivo and in vitro on various AChE-containing tissues (Karlsson et al., 1984; Lin et al., 1987), showed that i) FAS2 inhibits several (but not all) AChEs from different sources, ii) inhibition is of pseudo-irreversible type with Ki values of about 10⁻¹¹ M., iii) FAS2 is able to displace propidium, known as a specific probe for a peripheral anionic site of AChE (See Harvey et al., 1984 for a review).