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Ion- and water-binding sites inside an occluded hourglass pore of a trimeric intracellular cation (TRIC) channel.


ABSTRACT: Trimeric intracellular cation (TRIC) channels are crucial for Ca2+ handling in eukaryotes and are involved in K+ uptake in prokaryotes. Recent studies on the representative members of eukaryotic and prokaryotic TRIC channels demonstrated that they form homotrimeric units with the ion-conducting pores contained within each individual monomer.Here we report detailed insights into the ion- and water-binding sites inside the pore of a TRIC channel from Sulfolobus solfataricus (SsTRIC). Like the mammalian TRIC channels, SsTRIC is permeable to both K+ and Na+ with a slight preference for K+, and is nearly impermeable to Ca2+, Mg2+, or Cl-. In the 2.2-Å resolution K+-bound structure of SsTRIC, ion/water densities have been well resolved inside the pore. At the central region, a filter-like structure is shaped by the kinks on the second and fifth transmembrane helices and two nearby phenylalanine residues. Below the filter, the cytoplasmic vestibule is occluded by a plug-like motif attached to an array of pore-lining charged residues.The asymmetric filter-like structure at the pore center of SsTRIC might serve as the basis for the channel to bind and select monovalent cations. A Velcro-like plug-pore interacting model has been proposed and suggests a unified framework accounting for the gating mechanisms of prokaryotic and eukaryotic TRIC channels.

SUBMITTER: Ou X 

PROVIDER: S-EPMC5401562 | biostudies-literature | 2017 Apr

REPOSITORIES: biostudies-literature

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Ion- and water-binding sites inside an occluded hourglass pore of a trimeric intracellular cation (TRIC) channel.

Ou Xiaomin X   Guo Jianli J   Wang Longfei L   Yang Hanting H   Liu Xiuying X   Sun Jianyuan J   Liu Zhenfeng Z  

BMC biology 20170422 1


<h4>Background</h4>Trimeric intracellular cation (TRIC) channels are crucial for Ca<sup>2+</sup> handling in eukaryotes and are involved in K<sup>+</sup> uptake in prokaryotes. Recent studies on the representative members of eukaryotic and prokaryotic TRIC channels demonstrated that they form homotrimeric units with the ion-conducting pores contained within each individual monomer.<h4>Results</h4>Here we report detailed insights into the ion- and water-binding sites inside the pore of a TRIC cha  ...[more]

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