Cation-pi interactions: Difference between revisions

In 1998, Zhong ''et al.'' (with Dougherty)<ref name="zhong">PMID: 9770444</ref> provided evidence that the [http://en.wikipedia.org/wiki/Nicotinic_acetylcholine_receptor cation in '''acetylcholine'''] engages in a cation-pi interaction with Trp149 in the '''neuronal-type''' receptor, making an important contribution to the binding affinity. In 2002, Beene ''et al.'' (with Dougherty)<ref name="XD" /> provided evidence that no such cation-pi interaction is involved when '''nicotine''' binds to the '''muscle-type''' receptor, thus accounting in part for the lower affinity. In 2009, Xiu ''et al.''<ref name="XD" /> provided evidence that a strong cation-pi interaction occurs between the cation of '''nicotine''' and Trp149 in the '''neuronal-type''' receptor. The crystal structure of a molluscan acetylcholine-binding protein confirms the existence of a cation-pi interaction between the homologous Trp (Trp143) and the nicotine cation. The lower affinity of nicotine for the muscle-type, compared to the neuronal type receptors, is accounted for by differences in cation-pi interaction strength and the absence of a nicotine-receptor hydrogen bond in the former<ref name="XD" />.

===Examples from Gallivan and Dougherty<ref name='GD' />===