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Figure 1
The chemical structures of the physiological ligand of nAChRs (acetylcholine), a potent agonist (nicotine), two drugs that target these ion channels (cytisine and varenicline) and the natural products characterized in this study [(+)-anatoxin-a and (−)-hosieine-A]. The pKa of anatoxin-a is 9.4 (Koskinen & Rapoport, 1985BB28) and under the conditions in which we obtained crystals the ligand is likely to be protonated. The pKa values of cytisine, varenicline and nicotine are calculated to be 7.9, 9.7 and 8.5 (https://www.chemspider.com/), respectively, and by inference a similar value should apply to (−)-hosieine-A, hence we show the protonated forms that are expected to predominate at physiological pH.

Journal logoSTRUCTURAL BIOLOGY
COMMUNICATIONS
ISSN: 2053-230X
Volume 78| Part 9| September 2022| Pages 313-323
https://doi.org/10.1107/S2053230X22007762
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