Drysdalin, a snake neurotoxin with higher affinity for soluble acetylcholine binding protein from Aplysia californica than from Lymnaea stagnalis

Cytisine, a natural product with high affinity for clinically relevant nicotinic acetylcholine receptors (nAChRs), is used as a smoking-cessation agent. The compound displays an excellent clinical profile and hence there is an interest in derivatives that may be further improved or find use in the treatment of other conditions. Here, the binding of a cytisine derivative modified by the addition of a 3-(hydroxypropyl) moiety (ligand 4) to Aplysia californica acetylcholine-binding protein (AcAChBP), a surrogate for nAChR orthosteric binding sites, was investigated. Isothermal titration calorimetry revealed that the favorable binding of cytisine and its derivative to AcAChBP is driven by the enthalpic contribution, which dominates an unfavorable entropic component. Although ligand 4 had a less unfavorable entropic contribution compared with cytisine, the affinity for AcAChBP was significantly diminished owing to the magnitude of the reduction in the enthalpic component. The high-resolution crystal structure of the AcAChBP–4 complex indicated close similarities in the protein–ligand interactions involving the parts of 4 common to cytisine. The point of difference, the 3-(hydroxypropyl) substituent, appears to influence the conformation of the Met133 side chain and helps to form an ordered solvent structure at the edge of the orthosteric binding site.

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Virtual Screening against Acetylcholine Binding Protein

CrossRef Listing of Deleted DOIs ◽

10.1177/1087057111421667 ◽

2011 ◽

Vol 17 (2) ◽

pp. 204-215 ◽

Cited By ~ 8

Author(s):

Maleeruk Utsintong ◽

Piyanuch Rojsanga ◽

Kwok-Yiu Ho ◽

Todd T. Talley ◽

Arthur J. Olson ◽

...

Keyword(s):

Virtual Screening ◽

Nicotinic Acetylcholine Receptors ◽

Acetylcholine Receptors ◽

Lymnaea Stagnalis ◽

Binding Protein ◽

Resonance Energy Transfer ◽

Resonance Energy ◽

Acetylcholine Binding Protein ◽

Recombinant Receptors

The nicotinic acetylcholine receptors (nAChRs) are a member of the ligand-gated ion channel family and play a key role in the transfer of information across neurological networks. The X-ray crystal structure of agonist-bound α7 acetylcholine binding protein (AChBP) has been recognized as the most appropriate template to model the ligand-binding domain of nAChR for studying the molecular mechanism of the receptor–ligand interactions. Virtual screening of the National Cancer Institute diversity set, a library of 1990 compounds with nonredundant pharmacophore profiles, using AutoDock against AChBPs revealed 51 potential candidates. In vitro radioligand competition assays using [3H] epibatidine against the AChBPs from the freshwater snails, Lymnaea stagnalis, and from the marine species, Aplysia californica and the mutant (AcY55W), revealed seven compounds from the list of candidates that had micromolar to nanomolar affinities for the AChBPs. Further investigation on α7nAChR expressing in Xenopus oocytes and on the recombinant receptors with fluorescence resonance energy transfer (FRET)–based calcium sensor expressing in HEK cells showed that seven compounds were antagonists of α7nAChR, only one compound (NSC34352) demonstrated partial agonistic effect at low dose (10 µM), and two compounds (NSC36369 and NSC34352) were selective antagonists on α7nAchR with moderate potency. These hits serve as novel templates/scaffolds for development of more potent and specific in the AChR systems.

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