Figure 5.

Comparison of subunit interfaces. (A) Superposition of β2/α4 [in cyan or orange, respectively; PDB ID: 5KXI (Morales‐Perez et al., 2016)], α2/α2 [in green or yellow, respectively; PDB ID: 5FJV (Kouvatsos et al., 2016)] and nicotine‐bound AChBP [in purple or magenta, respectively; PDB ID: 1UW6 (Celie et al., 2004)]. The lack of one tyrosine in loop C of the β2 subunit allows the radical rotation of its Tyr¹⁹⁶ to occupy space that in α subunits is occupied by the other tyrosine (e.g. α2‐Tyr²¹⁹). β2‐Tyr¹⁹⁶ along with the β2‐Tyr⁹⁵ from loop A stabilize the β2‐Arg¹⁴⁹ that rams the cavity. This is possible only after β2‐Tyr⁹⁵ recedes towards the complementary subunit, occupying the space where in α subunits the loop‐B tryptophan (e.g. α2‐Trp¹⁷⁸) is found. As a result, β2‐Trp¹⁵¹ presents an extreme rotational movement towards β4–β5 loop. Notably, the α2‐ECD pentameric structure shows that this rotamer of loop‐B tryptophan is also possible in α subunits, but not in AChBPs where this space is occupied by β4–β5 loop. (B) The same as (A) rotated by 90^o. The coordinates of all the structures depicted were retrieved from Protein Data Bank (http://www.wwpdb.org), and PyMol (http://www.pymol.org) was used to generate the figures.