Protein engineering and design in ion channels and receptors

Acetylcholine receptors (AChRs) expressed at the neuromuscular junction synapses are typical allosteric proteins that shuttle between at least two stable conformational states: Closed (C) and Open (O). Agonist binding to their target sites on the receptor in the extracellular domain triggers a global C→O conformational change that results in an open channel pore that allows ion conduction. How the receptor senses the chemical signal of an agonist and communicates it to the channel pore, located ~50Å away, are key to understanding the receptor function. AChRs are indispensable for muscle contraction and their neuronal homologues play critical roles in the nervous system function. In this chapter, using a combination of single channel patch-clamp, computational approaches, and genetic engineering, we elucidate the principles of design and engineering to quantify the fundamental thermodynamic parameters of AChRs that regulate ligand binding and channel opening. The receptor engineering principles outlined here for the neuromuscular AChRs are applicable to the broader class of ligand-gated ion channel proteins.