Signaling at the neuromuscular synapse requires C(losed-channel)?O(pen-channel) 'gating'of acetylcholine receptors (AChRs). The thermodynamic foundation of this allosteric transition is well understood: transmitter molecules released from the nerve terminal bind to AChRs with higher affinity to O vs. C to increase the probability that the channel is Open. The microscopic events within C?O are less certain. We will use single-channel kinetics and phi-value analysis to probe the interior of AChR gating and illuminate the ultra-fast protein rearrangements within this reaction. So far, results show that AChRs change from C-to-O in 4 steps. The first amino acids to move are not at the transmitter binding sites but in a distant membrane domain linker that joins the M2 and M3 helices of the subunit. Further, the unlocking of a double-gate in M2 (all subunits) occurs in the final 2 gating activation steps. Most side chain gating movements are 'resettling'events that have only local energetic consequences. We will investigate two new hypotheses for AChR gating: 1) communication between the binding sites and the gate is not by a structural-mechanical process but, rather, by the vibrational entropy of the entire backbone, and 2) allosteric communication commences with low-affinity binding of the agonist to the resting receptor.
Chemical synaptic transmission requires the activation of membrane receptors by neurotransmitters. We will use the nerve-muscle synaptic receptor as a model system for understanding the mechanism of this activation. What we will learn increases our basic knowledge of molecular neuroscience, especially with regard to receptor physiology, pharmacology and diseases.
Showing the most recent 10 out of 12 publications
