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Articles by J Yao
Total Records ( 2 ) for J Yao
  A Nowack , J Yao , K. L Custer and S. M. Bajjalieh

Among the proteins that mediate calcium-stimulated transmitter release, the synaptic vesicle protein 2 (SV2) stands out as a unique modulator specific to the neurons and endocrine cells of vertebrates. In synapses, SV2 regulates the expression and trafficking of the calcium sensor protein synaptotagmin, an action consistent with the reduced calcium-mediated exocytosis observed in neurons lacking SV2. Yet SV2 contains amino acid motifs consistent with it performing other actions that could regulate presynaptic functioning and that might underlie the mechanism of drug action. To test the role of these functional motifs, we performed a mutagenic analysis of SV2A and assessed the ability of mutant SV2A proteins to restore normal synaptic transmission in neurons from SV2A/B knockout mice. We report that SV2A-R231Q, harboring a mutation in a canonical transporter motif, restored normal synaptic depression (a measure of release probability and signature deficit of neurons lacking SV2). In contrast, normal synaptic depression was not restored by SV2A-W300A and SV2A-W666A, harboring mutations of conserved tryptophans in the 5th and 10th transmembrane domains. Although they did not rescue normal neurotransmission, SV2A-W300A and SV2A-W666A did restore normal levels of synaptotagmin expression and internalization. This indicates that tryptophans 300 and 666 support an essential action of SV2 that is unrelated to its role in synaptotagmin expression or trafficking. These results indicate that SV2 performs at least two actions at the synapse that contribute to neurotransmitter release.

  B Liu , J Yao , Y Wang , H Li and F. Qin

Protons, which are released during inflammation and injury, regulate many receptors and ion channels involved in pain transduction, including capsaicin channels (transient receptor potential vanilloid receptors 1). Whereas extracellular acidification both sensitizes and directly activates the channel, it also causes concomitant reduction of the unitary current amplitudes. Here, we investigate the mechanisms and molecular basis of this inhibitory effect of protons on channel conductance. Single-channel recordings showed that the unitary current amplitudes decreased with extracellular pH in a dose-dependent manner, consistent with a model in which protons bind to a site within the channel with an apparent pKa of ~6. The inhibition was voltage dependent, ~65% at –60 mV and 37% at +60 mV when pH was reduced from 7.4 to 5.5. The unitary current amplitudes reached saturation at [K+] ≥ 1 M, and notably the maximum amplitudes did not converge with different pHs, inconsistent with a blockade model based on surface charge screening or competitive inhibition of permeating ions. Mutagenesis experiments uncovered two acidic residues critical for proton inhibition, one located at the pore entrance and the other on the pore helix. Based on homology to the KcsA structure, the two acidic residues, along with another basic residue also on the pore helix, could form a triad interacting with each other through extensive hydrogen bonds and electrostatic contacts, suggesting that protons may mediate the interactions between the selectivity filter and pore helix, thereby altering the local structure in the filter region and consequently the conductance of the channel.

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