The assembly of bound glycolipids and extraneous hydrocarbons, if present in the GLTP tunnel, are shown. The bordered segment labeled 1 encompasses the sugar- and amide-binding site on the GLTP, whereas bordered segments 2 and 3 span lipid-binding sites within the hydrophobic GLTP tunnel. The narrow bottom of the GLTP tunnel is schematically represented by a transparent cylinder, labeled 2. The segment labeled 3 is collapsed in apo-GLTP and its complex with n-hexyl-β-d-glucoside. The glycolipid atoms are colored red and blue for oxygen and nitrogen atoms, respectively, and by specific colors for carbon and extraneous hydrocarbons. Specific colors are green for 24:1 GalCer, cyan for 8:0 LacCer, lavender for 18:1 LacCer, lemon for 18:2 GalCer, and silver for extraneous hydrocarbons accompanying 8:0 LacCer, 18:2 LacCer, and apo-GLTP. The longest extraneous hydrocarbon, which is the only one entering the region labeled 3, accompanies 8:0 LacCer.