Conformational Flexibility in the Peripheral Site of Torpedo californica Acetylcholinesterase Revealed by the Complex Structure with a Bifunctional Inhibitor

摘要

X-ray crystallography is a powerful tool that provides time-averaged pictures of biological macromolecules.These seemingly static structures are in reality animated by molecular motions stemming from transitions between substates in a conformational energy landscape.This landscape is characterized by a very large number of conformational substates,the population of which depends on their free energy.A crystallographic structure represents only the predominant substate of a molecule,and minor populations can usually not be assessed.Yet,the understanding of biological function on a molecular level requires knowledge about both structural and dynamical aspects of,e.g.,an enzyme.This is particularly obvious for acetylcholinesterase (AChE),the active site of which is accessed by a deep and narrow gorge that makes "breathing" motions essential for traffic of substrates and products to occur.Here,we report the X-ray crystallographic structure of AChE from Torpedo californica (TcAChE) in complex with a gorge-spanning inhibitor,NF595 (Figure 1).NF595 has been synthesized with a view to developing a new generation of anti-Alzheimer drugs,interacting with both the active and peripheral binding sites of AChEs.Surprisingly,and for the first time in TcAChE,a major conformational change is observed upon com-plexation in the peripheral substrate-binding site.We suggest that this conformational substate is part of the equilibrium dynamics of the native enzyme and that it has been selected by inhibitor binding.