2q68: Difference between revisions
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'''Crystal Structure of Nak channel D66A, S70E double mutants''' | '''Crystal Structure of Nak channel D66A, S70E double mutants''' | ||
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[[Category: Jiang, Y.]] | [[Category: Jiang, Y.]] | ||
[[Category: Shi, N.]] | [[Category: Shi, N.]] | ||
[[Category: | [[Category: Central cavity]] | ||
[[Category: | [[Category: Helix bundle]] | ||
[[Category: | [[Category: Inverted teepee]] | ||
[[Category: | [[Category: Ion binding]] | ||
[[Category: | [[Category: Membrane protein]] | ||
[[Category: | [[Category: Metal transport]] | ||
[[Category: | [[Category: Tetramer]] | ||
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Revision as of 14:25, 4 May 2008
Crystal Structure of Nak channel D66A, S70E double mutants
OverviewOverview
Apparent blockage of monovalent cation currents by the permeating blocker Ca(2+) is a physiologically essential phenomenon relevant to cyclic nucleotide-gated (CNG) channels. The recently determined crystal structure of a bacterial homolog of CNG channel pores, the NaK channel, revealed a Ca(2+) binding site at the extracellular entrance to the selectivity filter. This site is not formed by the side-chain carboxylate groups from the conserved acidic residue, Asp-66 in NaK, conventionally thought to directly chelate Ca(2+) in CNG channels, but rather by the backbone carbonyl groups of residue Gly-67. Here we present a detailed structural analysis of the NaK channel with a focus on Ca(2+) permeability and blockage. Our results confirm that the Asp-66 residue, although not involved in direct chelation of Ca(2+), plays an essential role in external Ca(2+) binding. Furthermore, we give evidence for the presence of a second Ca(2+) binding site within the NaK selectivity filter where monovalent cations also bind, providing a structural basis for Ca(2+) permeation through the NaK pore. Compared with other Ca(2+)-binding proteins, both sites in NaK present a novel mode of Ca(2+) chelation, using only backbone carbonyl oxygen atoms from residues in the selectivity filter. The external site is under indirect control by an acidic residue (Asp-66), making it Ca(2+)-specific. These findings give us a glimpse of the possible underlying mechanisms allowing Ca(2+) to act both as a permeating ion and blocker of CNG channels and raise the possibility of a similar chemistry governing Ca(2+) chelation in Ca(2+) channels.
About this StructureAbout this Structure
2Q68 is a Single protein structure of sequence from Bacillus cereus. Full crystallographic information is available from OCA.
ReferenceReference
Structural insight into Ca2+ specificity in tetrameric cation channels., Alam A, Shi N, Jiang Y, Proc Natl Acad Sci U S A. 2007 Sep 25;104(39):15334-9. Epub 2007 Sep 18. PMID:17878296 Page seeded by OCA on Sun May 4 14:25:33 2008