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1.  Recent Structural and Mechanistic Insights into Endplate Acetylcholine Receptors 
Voluntary movement mediated by skeletal muscle relies on endplate acetylcholine receptors (AChR) to detect nerve-released ACh and depolarize themuscle fiber. Recent structural and mechanistic studies of the endplate AChR have catalyzed a leap in our understanding of the molecular steps in this chemical-to-electrical transduction process. Studies of acetylcholine binding protein (AChBP) give insight into ACh recognition, the first step in activation of the AChR. An atomic structural model of the Torpedo AChR at a resolution of 0.4 nm, together with single-ion channel recording methods, allow tracing of the link between the agonist binding event and gating of the ion channel, as well as determination of how the channel moves when it opens to allow flow of cations. Structural models of the human AChR enable precise mapping of disease-causing mutations, while studies of the speed with which single AChR channels open and close cast light on pathogenic mechanisms.
PMCID: PMC3478106  PMID: 18567853
acetylcholine receptor; acetylcholine binding protein; agonist recognition; binding-gating coupling mechanism; congenital myasthenic syndrome
2.  Detection and Trapping of Intermediate States Priming Nicotinic Receptor Channel Opening 
Nature  2009;459(7245):451-454.
In the course of synaptic transmission in the brain and periphery, acetylcholine receptors (AChRs) rapidly transduce a chemical signal into an electrical impulse. The speed of transduction owes in large part to rapid ACh association and dissociation, implying a binding site relatively non-selective for small cations; selective transduction has been supposed to originate from the ability of ACh, over that of other organic cations, to trigger the subsequent channel opening step. However transitions to and from the open state were shown to be similar for agonists with widely different efficacies.1,2,3 Here, by studying mutant AChRs, we find that the ultimate closed to open transition is agonist-independent and preceded by two primed closed states; the first primed state elicits brief openings, whereas the second elicits long-lived openings. Long-lived openings and the associated primed state are detected in the absence and presence of agonist, and exhibit the same kinetic signatures under both conditions. By covalently locking the agonist binding sites in the bound conformation, we find that each site initiates a priming step. Thus a change in binding site conformation primes the AChR for channel opening in a process that enables selective activation by ACh while maximizing speed and efficiency of the biological response.
PMCID: PMC2712348  PMID: 19339970
3.  Initial Coupling of Binding to Gating Mediated by Conserved Residues in the Muscle Nicotinic Receptor 
We examined functional consequences of intrasubunit contacts in the nicotinic receptor α subunit using single channel kinetic analysis, site-directed mutagenesis, and structural modeling. At the periphery of the ACh binding site, our structural model shows that side chains of the conserved residues αK145, αD200, and αY190 converge to form putative electrostatic interactions. Structurally conservative mutations of each residue profoundly impair gating of the receptor channel, primarily by slowing the rate of channel opening. The combined mutations αD200N and αK145Q impair channel gating to the same extent as either single mutation, while αK145E counteracts the impaired gating due to αD200K, further suggesting electrostatic interaction between these residues. Interpreted in light of the crystal structure of acetylcholine binding protein (AChBP) with bound carbamylcholine (CCh), the results suggest in the absence of ACh, αK145 and αD200 form a salt bridge associated with the closed state of the channel. When ACh binds, αY190 moves toward the center of the binding cleft to stabilize the agonist, and its aromatic hydroxyl group approaches αK145, which in turn loosens its contact with αD200. The positional changes of αK145 and αD200 are proposed to initiate the cascade of perturbations that opens the receptor channel: the first perturbation is of β-strand 7, which harbors αK145 and is part of the signature Cys-loop, and the second is of β-strand 10, which harbors αD200 and connects to the M1 domain. Thus, interplay between these three conserved residues relays the initial conformational change from the ACh binding site toward the ion channel.
PMCID: PMC2266616  PMID: 15955875

Results 1-3 (3)