J Am Chem Soc 2019 Oct 09;14140:15840-15849. doi: 10.1021/jacs.9b06580.

Probing Binding Interactions of Cytisine Derivatives to the α4β2 Nicotinic Acetylcholine Receptor.

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Nicotinic acetylcholine receptors (nAChRs) are crucial for communication between synapses in the central nervous system. As such, they are also implicated in several neuropsychiatric and addictive diseases. Cytisine is a partial agonist of some nAChRs and has been used for smoking cessation. Previous studies have established a binding model for several agonists to several nAChR subtypes. Here, we evaluate the extent to which this model applies to cytisine at the α4β2 nAChR, which is a subtype that is known to play a prominent role in nicotine addiction. Along with the commonly seen cation-π interaction and two hydrogen bonds, we find that cytisine makes a second cation-π interaction at the agonist binding site. We also evaluated a series of C(10)-substituted cytisine derivatives, using two-electrode voltage-clamp electrophysiology and noncanonical amino acid mutagenesis. Double-mutant cycle analyses revealed that C(10) substitution generally strengthens the newly established second cation-π interaction, while it weakens the hydrogen bond typically seen to LeuE in the complementary subunit. The results suggest a model for how cytisine derivatives substituted at C(10) (as well as C(9)/C(10)) adjust their binding orientation, in response to pyridone ring substitution.

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