The structure of AChBP is illustrated over a representation of the transmembrane domain of nAChR. Each subunit (α, β, γ or ε, δ) is labeled by its Greek symbol. The α subunit is shown in yellow, except for most of the signature cys-loop, which is shown in red, and AChBP G127 is shown in green (this residue aligns with nAChRα V132). The membrane spanning regions M1–M3 are represented on the bilayer surface, and M4 is also shown in cross section.