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Articles by Z. Lu
Total Records ( 4 ) for Z. Lu
  H. Jin , F. Zhiyi , Z. Yang , C. Ruicheng and Z. Lu
  In broadcast and mobile systems, large-scale and scalable protocols are needed to guarantee reliability and provide function of congestion control. ALC (Asynchronous Layered Coding) was designed to meet that, Nonetheless, the drawbacks of it are obviously such as the end-to-end reliability can`t be guaranteed, the document to be sent and its attributes are separated. So, FLUTE (File Delivery over Unidirectional Transport) is defined based on ALC which can avoid the shortcomings of ALC by the mechanism of FDT. In this study, we tested and evaluated the client-side programs based on FLUTE to confirm that it can meet the user’s needs. The correctness of the software exploited in this study also has been proved by applying in the European Union`s INSTINCT- WORLD project.
  J. R Martinez Francois , Y Xu and Z. Lu
 

Activity of cyclic nucleotide–gated (CNG) cation channels underlies signal transduction in vertebrate visual receptors. These highly specialized receptor channels open when they bind cyclic GMP (cGMP). Here, we find that certain mutations restricted to the region around the ion selectivity filter render the channels essentially fully voltage gated, in such a manner that the channels remain mostly closed at physiological voltages, even in the presence of saturating concentrations of cGMP. This voltage-dependent gating resembles the selectivity filter-based mechanism seen in KcsA K+ channels, not the S4-based mechanism of voltage-gated K+ channels. Mutations that render CNG channels gated by voltage loosen the attachment of the selectivity filter to its surrounding structure, thereby shifting the channel's gating equilibrium toward closed conformations. Significant pore opening in mutant channels occurs only when positive voltages drive the pore from a low-probability open conformation toward a second open conformation to increase the channels' open probability. Thus, the structure surrounding the selectivity filter has evolved to (nearly completely) suppress the expression of inherent voltage-dependent gating of CNGA1, ensuring that the binding of cGMP by itself suffices to open the channels at physiological voltages.

  J. R Martinez Francois , Y Xu and Z. Lu
 

Cyclic nucleotide–gated channels mediate transduction of light into electric signals in vertebrate photoreceptors. These channels are primarily controlled by the binding of intracellular cyclic GMP (cGMP). Glutamate residue 363 near the extracellular end of the ion selectivity filter interacts with the pore helix and helps anchor the filter to the helix. Disruption of this interaction by mutations renders the channels essentially fully voltage gated in the presence of saturating concentrations of cGMP. Here, we find that lowering extracellular pH makes the channels conduct in an extremely outwardly rectifying manner, as does a neutral glutamine substitution at E363. A pair of cysteine mutations, E363C and L356C (the latter located midway the pore helix), largely eliminates current rectification at low pH. Therefore, this low pH-induced rectification primarily reflects voltage-dependent gating involving the ion selectivity filter rather than altered electrostatics around the external opening of the ion pore and thus ion conduction. It then follows that protonation of E363, like the E363Q mutation, disrupts the attachment of the selectivity filter to the pore helix. Loosening the selectivity filter from its surrounding structure shifts the gating equilibrium toward closed states. At low extracellular pH, significant channel opening occurs only when positive voltages drive the pore from a low probability open conformation to a second open conformation. Consequently, at low extracellular pH the channels become practically fully voltage gated, even in the presence of a saturating concentration of cGMP.

 
 
 
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