PDB-5ke4: Crystal structure of a chimeric acetylcholine binding protein from Aplysia californica (Ac-AChBP) containing loop C from the human alpha 6 nicotinic acetylcholine receptor in complex with 2-((5-(3,7-Diazabicyclo[3.3.1]nonan-3-yl)pyridin-3-yl)oxy)- N,N-dimethylethanamine (BPC)