Neurotransmitter receptors from the Cys-loop superfamily couple the binding of agonist to the opening of an intrinsic ion pore in the final step in rapid synaptic transmission. Although atomic resolution structural data have recently emerged for individual binding and pore domains, how they are linked into a functional unit remains unknown. Here we identify structural requirements for functionally coupling the two domains by combining acetylcholine (ACh)-binding protein, whose structure was determined at atomic resolution, with the pore domain from the serotonin type-3A (5-HT3A) receptor. Only when amino-acid sequences of three loops in ACh-binding protein are changed to their 5-HT3A counterparts does ACh bind with low affinity characteristic of activatable receptors, and trigger opening of the ion pore. Thus functional coupling requires structural compatibility at the interface of the binding and pore domains. Structural modelling reveals a network of interacting loops between binding and pore domains that mediates this allosteric coupling process.

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.

We describe the genetic and kinetic defects for a low-affinity fast channel disease of the acetylcholine receptor (AChR) that causes a myasthenic syndrome. In two unrelated patients with very small miniature end plate (EP) potentials, but with normal EP AChR density and normal EP ultrastructure, patch-clamp studies demonstrated infrequent AChR channel events, diminished channel reopenings during ACh occupancy, and resistance to desensitization by ACh. Each patient had two heteroallelic AChR epsilon subunit gene mutations: a common epsilon P121L mutation, a signal peptide mutation (epsilon G-8R) (patient 1), and a glycosylation consensus site mutation (epsilon S143L) (patient 2). AChR expression in HEK fibroblasts was normal with epsilon P121L but was markedly reduced with the other mutations. Therefore, epsilon P121L defines the clinical phenotype. Studies of the engineered epsilon P121L AChR revealed a markedly decreased rate of channel opening, little change in affinity of the resting state for ACh, but reduced affinity of the open channel and desensitized states.

Soil contamination with heavy metals and organic pollutants has increasingly become a serious global environmental issue in recent years. Considerable efforts have been made to remediate contaminated soils. Biochar has a large surface area, and high capacity to adsorb heavy metals and organic pollutants. Biochar can potentially be used to reduce the bioavailability and leachability of heavy metals and organic pollutants in soils through adsorption and other physicochemical reactions. Biochar is typically an alkaline material which can increase soil pH and contribute to stabilization of heavy metals. Application of biochar for remediation of contaminated soils may provide a new solution to the soil pollution problem. This paper provides an overview on the impact of biochar on the environmental fate and mobility of heavy metals and organic pollutants in contaminated soils and its implication for remediation of contaminated soils. Further research directions are identified to ensure a safe and sustainable use of biochar as a soil amendment for remediation of contaminated soils.

We previously identified lynx1 as a neuronal membrane molecule related to snake alpha-neurotoxins able to modulate nAChRs. Here, we show that lynx1 colocalizes with nAChRs on CNS neurons and physically associates with nAChRs. Single-channel recordings show that lynx1 promotes the largest of three current amplitudes elicited by ACh through alpha(4)beta(2) nAChRs and that lynx1 enhances desensitization. Macroscopic recordings quantify the enhancement of desensitization onset by lynx1 and further show that it slows recovery from desensitization and increases the EC(50). These experiments establish that direct interaction of lynx1 with nAChRs can result in a novel type of functional modulation and suggest that prototoxins may play important roles in vivo by modulating functional properties of their cognate CNS receptors.