Structural correlates of affinity in fetal versus adult endplate nicotinic receptors

• Published in: Nature communications Vol. 7; no. 1; p. 11352
• Main Authors: Nayak, Tapan Kumar, Chakraborty, Srirupa, Zheng, Wenjun, Auerbach, Anthony
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 22.04.2016; Nature Publishing Group; Nature Portfolio
• Subjects: 13; 13/106; 13/109; 14; 14/63; 38; 38/70; 38/77; 631/378; 631/45/269/1149; 631/45/535; 631/57/2272; 9/74; Acetylcholine receptors (nicotinic); Affinity; Age Factors; Amino Acid Motifs; Amino acids; Animals; Aplysia - chemistry; Binding Sites; Computer simulation; Crystallography, X-Ray; Electrophysiology; Excitatory Postsynaptic Potentials - physiology; Fetuses; Gene Expression; HEK293 Cells; Homology; Humanities and Social Sciences; Humans; Mice; Molecular dynamics; Molecular Dynamics Simulation; Molecular Sequence Data; multidisciplinary; Neuromuscular junctions; Protein Binding; Protein Structure, Secondary; Protein Structure, Tertiary; Protein Subunits - chemistry; Protein Subunits - genetics; Protein Subunits - metabolism; Receptors; Receptors, Nicotinic - chemistry; Receptors, Nicotinic - genetics; Receptors, Nicotinic - metabolism; Recombinant Proteins - chemistry; Recombinant Proteins - genetics; Recombinant Proteins - metabolism; Residues; Science; Sequence Alignment; Signal Transduction; Structural Homology, Protein; Tryptophan
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms11352

Adult-type nicotinic acetylcholine receptors (AChRs) mediate signalling at mature neuromuscular junctions and fetal-type AChRs are necessary for proper synapse development. Each AChR has two neurotransmitter binding sites located at the interface of a principal and a complementary subunit. Although all agonist binding sites have the same core of five aromatic amino acids, the fetal site has ∼30-fold higher affinity for the neurotransmitter ACh. Here we use molecular dynamics simulations of adult versus fetal homology models to identify complementary-subunit residues near the core that influence affinity, and use single-channel electrophysiology to corroborate the results. Four residues in combination determine adult versus fetal affinity. Simulations suggest that at lower-affinity sites, one of these unsettles the core directly and the others (in loop E) increase backbone flexibility to unlock a key, complementary tryptophan from the core. Swapping only four amino acids is necessary and sufficient to exchange function between adult and fetal AChRs. Adult and fetal nicotinic acetylcholine receptors (AChRs) have different functional requirements and affinity for ACh. Here, the authors use molecular dynamics and electrophysiology to investigate this affinity, and identify four amino acids that when swapped exchange function between adult and fetal AChRs.