3-D structure of the human α4β2 nAChR (from Protein Data Bank accession no. 5KXI ; Morales-Perez et al., 2016 ) showing direction of N-terminal α-helix and modeled linkers. The α4 subunit is colored green, and β2 is blue. (A) Top view of the (α4)2(β2)3 receptor with the N-terminal helixes shown in red. (B) Top view of the α4β2 dimer with the N-terminal LLxxLF motif shown as red spheres. The surface of the protein constituting hydrophobic residues on the top of the α4 and β2 subunits is colored yellow. The LLxxLF motif interacts with the hydrophobic surface to form a hydrophobic patch. (C) α4β2 dimer with modeled long clockwise and short counterclockwise linkers. The shortest possible number of AGS repeats required to connect the first residue after TM4 of the β2 subunit (Leu479) to the mature N terminus of α4 (Ala34) is shown and had lengths of 10 and 8 repeats, respectively. (D) Illustration of total linker length calculations for new concatenated β-xa-α dimer constructs. Note that only parts of the cDNA sequences close to the linkers are shown.
