Fig. 4.

Amino acids playing a critical role in the interactions with nicotine in the crystal structure of Ls acetylcholine binding protein (PDB, 1UV6). The picture was generated using Sybyl (version 7.1; Tripos Associates, Inc.). Note that nicotine is captured by a hydrogen bond between NH and the backbone of Trp143 as well as a CH-π interaction between N⁺CH₂-H and the tryptophan ring. The backbone of the principal side donating loops A to C is colored yellow, whereas that of the complementary side donating loops D to F is colored cyan. Nic, nicotine; HB, hydrogen bond.