Journal Article

Functional differences between neurotransmitter binding sites of muscle acetylcholine receptors

Chakraborty, Srirupa, Gupta, Shaweta, Nayak, Tapan K., Bruhova, Iva, Auerbach, Anthony, Zheng, Wenjun

2014

Overview

A muscle acetylcholine receptor (AChR) has two neurotransmitter binding sites located in the extracellular domain, at αδ and either αε (adult) or αγ (fetal) subunit interfaces. We used single-channel electrophysiology to measure the effects of mutations of five conserved aromatic residues at each site with regard to their contribution to the difference in free energy of agonist binding to active versus resting receptors (ΔGB1). The two binding sites behave independently in both adult and fetal AChRs. For four different agonists, including ACh and choline, ΔGB1 is~—2 kcal/mol more favorable at αγ compared with at αε and αδ. Only three of the aromatics contribute significantly to ΔGB1 at the adult sites (αγ190, αγ198, and aW149), but all five do so at αγ (as well as aY93 and γW55). γW55 makes a particularly large contribution only at αγ that is coupled energetically to those contributions of some of the a-subunit aromatics. The hydroxyl and benzene groups of loop C residues aY190 and aY198 behave similarly with regard to ΔGB1 at all three kinds of site. ACh binding energies estimated from molecular dynamics simulations are consistent with experimental values from electrophysiology and suggest that the αγ site is more compact, better organized, and less dynamic than αε and αδ. We speculate that the different sensitivities of the fetal αγ site versus the adult αε and αδ sites to choline and ACh are important for the proper maturation and function of the neuromuscular synapse.

• Publisher: National Academy of Sciences,National Acad Sciences
• Subject: Acetylcholine - metabolism / adults / Agonists / Animals / Benzene / Binding Sites / Biological Sciences / Choline - chemistry / Cholinergic receptors / Computer Simulation / Electrophysiology / energy / Free energy / Gene Expression Regulation, Developmental / HEK293 Cells / Humans / Hydrolysis / Ligands / Lymnaea / Maturation / Mice / Molecular Conformation / molecular dynamics / Molecular Dynamics Simulation / muscles / Muscles - metabolism / Mutation / Neurons / Neurotransmitter Agents - chemistry / Neurotransmitters / Nicotinic receptors / Protein Binding / Receptors / Receptors, Cholinergic - chemistry / Receptors, Cholinergic - physiology / synapse / Synapses / Synaptic Transmission / Thermodynamics / Torpedo / Tryptophan - chemistry