2ahz

File:2ahz.gif

K+ complex of the NaK Channel

Overview

Ion selectivity is one of the basic properties that define an ion channel. Most tetrameric cation channels, which include the K+, Ca2+, Na+ and cyclic nucleotide-gated channels, probably share a similar overall architecture in their ion-conduction pore, but the structural details that determine ion selection are different. Although K+ channel selectivity has been well studied from a structural perspective, little is known about the structure of other cation channels. Here we present crystal structures of the NaK channel from Bacillus cereus, a non-selective tetrameric cation channel, in its Na+- and K+-bound states at 2.4 A and 2.8 A resolution, respectively. The NaK channel shares high sequence homology and a similar overall structure with the bacterial KcsA K+ channel, but its selectivity filter adopts a different architecture. Unlike a K+ channel selectivity filter, which contains four equivalent K+-binding sites, the selectivity filter of the NaK channel preserves the two cation-binding sites equivalent to sites 3 and 4 of a K+ channel, whereas the region corresponding to sites 1 and 2 of a K+ channel becomes a vestibule in which ions can diffuse but not bind specifically. Functional analysis using an 86Rb flux assay shows that the NaK channel can conduct both Na+ and K+ ions. We conclude that the sequence of the NaK selectivity filter resembles that of a cyclic nucleotide-gated channel and its structure may represent that of a cyclic nucleotide-gated channel pore.

About this Structure

2AHZ is a Single protein structure of sequence from Bacillus cereus. Full crystallographic information is available from OCA.

Reference

Atomic structure of a Na+- and K+-conducting channel., Shi N, Ye S, Alam A, Chen L, Jiang Y, Nature. 2006 Mar 23;440(7083):570-4. Epub 2006 Feb 8. PMID:16467789 Page seeded by OCA on Sat May 3 19:04:30 2008

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