Fully flexible docking models of the complex between α7 nicotinic receptor and a potent heptapeptide inhibitor of the β-amyloid peptide binding

Two neuronal nicotinic acetylcholine receptors, alpha4beta4 and alpha7, show differential agonist binding modes

Nicotinic acetylcholine receptors (nAChRs) are pentameric, neurotransmitter-gated ion channels responsible for rapid excitatory neurotransmission in the central and peripheral nervous systems, resulting in skeletal muscle tone and various cognitive effects in the brain. These complex proteins are activated by the endogenous neurotransmitter ACh as well as by nicotine and structurally related agonists. Activation and modulation of nAChRs has been implicated in the pathology of multiple neurological disorders, and as such, these proteins are established therapeutic targets. Here we use unnatural amino acid mutagenesis to examine the ligand binding mechanisms of two homologous neuronal nAChRs: the α4β4 and α7 receptors. Despite sequence identity among the residues that form the core of the agonist-binding site, we find that the α4β4 and α7 nAChRs employ different agonist-receptor binding interactions in this region. The α4β4 receptor utilizes a strong cation-π interaction to a conserved tryptophan (TrpB) of the receptor for both ACh and nicotine, and nicotine participates in a strong hydrogen bond with a backbone carbonyl contributed by TrpB. Interestingly, we find that the α7 receptor also employs a cation-π interaction for ligand recognition, but the site has moved to a different aromatic amino acid of the agonist-binding site depending on the agonist. ACh participates in a cation-π interaction with TyrA, whereas epibatidine participates in a cation-π interaction with TyrC2.

Modeling peptide-protein interactions

Peptide-protein interactions are prevalent in the living cell and form a key component of the overall protein-protein interaction network. These interactions are drawing increasing interest due to their part in signaling and regulation, and are thus attractive targets for computational structural modeling. Here we report an overview of current techniques for the high resolution modeling of peptide-protein complexes. We dissect this complicated challenge into several smaller subproblems, namely: modeling the receptor protein, predicting the peptide binding site, sampling an initial peptide backbone conformation and the final refinement of the peptide within the receptor binding site. For each of these conceptual stages, we present available tools, approaches, and their reported performance. We summarize with an illustrative example of this process, highlighting the success and current challenges still facing the automated blind modeling of peptide-protein interactions. We believe that the upcoming years will see considerable progress in our ability to create accurate models of peptide-protein interactions, with applications in binding-specificity prediction, rational design of peptide-mediated interactions and the usage of peptides as therapeutic agents.

DMXB (GTS-21) ameliorates the cognitive deficits in beta amyloid(25-35(-) ) injected mice through preventing the dysfunction of alpha7 nicotinic receptor

Intracerebroventricular injection of beta-amyloid(25-35) (Abeta(25-35)) in mice leads to cognitive deficits with the dysfunction of alpha7 nicotinic acetylcholine receptor (alpha7nAChR) within 1-2 weeks in a dose-dependent manner. The present study focused on the effect of DMXB, a selective alpha7nAChR agonist, on Abeta(25-35) (3 nmol)-impaired spatial memory and alpha7nAChR function. We found that the treatment with DMXB on days 1-10 after Abeta(25-35) injection dose-dependently prevented Abeta(25-35)-induced impairment of acquisition performance and probe trail test in Morris water maze. Importantly, the treatment with DMXB (1 mg/kg) perfectly prevented Abeta(25-35)-induced depression of alpha7nAChR response, which was associated with improving the probability of presynaptic glutamate release and the induction of high-frequency stimulation (HFS)-dependent long-term potentiation (LTP) in hippocampal Schaffer collaterale-CA1 synapse. Furthermore, although either the basal level of extracellular signal-regulated kinase 2 (ERK2) or its phosphorylation in the hippocampus had no difference between control and Abeta(25-35) mice, the Abeta(25-35) injection significantly attenuated HFS-triggered increase in ERK2 phosphorylation. The treatment with DMXB also rescued the ERK2 phosphorylation triggered by HFS in Abeta(25-35) mice that is required for LTP induction. This study firstly provides in vivo evidence that the anti-amnesic effect of DMXB is likely due to preventing the Abeta(25-35)-induced dysfunction of alpha7nAChR.

The ?-amyloid protein of Alzheimer?s disease binds to membrane lipids but does not bind to the ?7 nicotinic acetylcholine receptor

Accumulation of the amyloid protein (Abeta) in the brain is an important step in the pathogenesis of Alzheimer's disease. However, the mechanism by which Abeta exerts its neurotoxic effect is largely unknown. It has been suggested that the peptide can bind to the alpha7 nicotinic acetylcholine receptor (alpha7nAChR). In this study, we examined the binding of Abeta1-42 to endogenous and recombinantly expressed alpha7nAChRs. Abeta1-42 did neither inhibit the specific binding of alpha7nAChR ligands to rat brain homogenate or slice preparations, nor did it influence the activity of alpha7nAChRs expressed in Xenopus oocytes. Similarly, Abeta1-42 did not compete for alpha-bungarotoxin-binding sites on SH-SY5Y cells stably expressing alpha7nAChRs. The effect of the Abeta1-42 on tau phosphorylation was also examined. Although Abeta1-42 altered tau phosphorylation in alpha7nAChR-transfected SH-SY5Y cells, the effect of the peptide was unrelated to alpha7nAChR expression or activity. Binding studies using surface plasmon resonance indicated that the majority of the Abeta bound to membrane lipid, rather than to a protein component. Fluorescence anisotropy experiments indicated that Abeta may disrupt membrane lipid structure or fluidity. We conclude that the effects of Abeta are unlikely to be mediated by direct binding to the alpha7nAChR. Instead, we speculate that Abeta may exert its effects by altering the packing of lipids within the plasma membrane, which could, in turn, influence the function of a variety of receptors and channels on the cell surface.