HCR/D-SA (blue, upper) includes conserved Phe1280 and Trp1282 (black), and the Ganglioside Binding Loop (GBL) is enlarged, rotated, (lower) and aligned with the structurally analogous β-hairpin loops of BoNT/A (purple), /B (orange), /C (red), /D (green). HCR/C and /D-SA loops. Note, BoNT/B has an extended β-hairpin loop like HCR/C, HCR/D, and HCR/D-SA, but lacks a tryptophan residue. BoNT/A, in contrast, does not have an extended β-hairpin loop. Reproduced from [62] with permission.