Structural correlates of affinity in fetal versus adult endplate nicotinic receptors.
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.
Department of Physiology and Biophysics, State University of New York at Buffalo, Buffalo, New York 14214, USA.
Tapan Kumar
TK
Nayak
Department of Physiology and Biophysics, State University of New York at Buffalo, Buffalo, New York 14214, USA.
Srirupa
S
Chakraborty
Department of Physics, State University of New York at Buffalo, Buffalo, New York 14260, USA.
Wenjun
W
Zheng
Department of Physiology and Biophysics, State University of New York at Buffalo, Buffalo, New York 14214, USA.
Anthony
A
Auerbach
D000367:Age Factors; D020816:Amino Acid Motifs; D000818:Animals; D001048:Aplysia / Q000737:chemistry; D001665:Binding Sites; D018360:Crystallography, X-Ray; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology*; D015870:Gene Expression; D057809:HEK293 Cells; D006801:Humans; D051379:Mice; D056004:Molecular Dynamics Simulation; D008969:Molecular Sequence Data; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011978:Receptors, Nicotinic / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D015398:Signal Transduction; D040681:Structural Homology, Protein
D021122:Protein Subunits; D011978:Receptors, Nicotinic; D011994:Recombinant Proteins