The ligand binding/unbinding process is critical to our understanding of the pharmacology of both the nicotinic
acetylcholine receptor (nAChR) and the acetylcholine binding protein (AChBP). Steered molecular dynamics
simulations were performed to learn about the unbinding process of the full agonist nicotine. Three different
pulling models were designed to investigate the possible binding/unbinding pathways: radial and tangent
models, and also a mixed model. Of the three, the tangent pulling model finally failed to dissociate nicotine
from the ligand binding pocket. The efficiency of the pulling force profiles was superior, and the opening of
the C-loop was smaller in the mixed pulling model than that in the radial model. The most favorable pathway
for the cholinergic agonist nicotine to enter or leave the binding pocket is through the principal binding side,
following a curvilinear track. Noticeably, it has been seen that the unbinding of the nicotine is concomitant
with a global rotation of the protein-ligand complex which could be caused by the interactions of the ligand
with protein at the tangent direction.