The second and smallest cluster of drugs binds in the middle of the tunnel. Although we consider this group to be a cluster, the binding positions of the drugs at the extremes of the cluster differ by 10 Å: ZINC000004099004 binds 26 Å from the surface, while ZINC000008214470 binds at 36 Å. The final region of the tunnel is also the most populated; 99.5% of the drugs tested in the virtual screen bind most strongly in its deepest third, between 45 Å and 65 Å from the surface. All of the top ten drugs identified in this study (Figure ) belong to this final cluster (Electronic Supporting Information -ESI) and have consistently lower binding energies than any drug binding preferentially in the other two regions. In addition, most of the drugs with the lowest binding energies belong to the cluster binding at position 3 (ESI). The profile of the tunnel in this region is narrower than in the other tunnel regions.