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Introduction
Ion channels are transmembrane proteins which allow ions to pass through biological membranes. Some of these channels are very selective, others have a low level of selectivity. The NaK channel is a non-selective one : It conduits cations more than anions but it let pass several cations : Na+, K+, Rb+, and Ca2+ [1.1].
Understanding how these channels work is important because in the organism a lot of messages are transmitted through electric currents (which are ionic currents across the membrane) : nerves impulse, photoreceptors, etc. Thus, these not very selective NaK channels are very interesting for the inhibition of intercellular messages for instance.
Structure
Active Site & Ions Passing
There are 4 ions binding sites in the NaK channel [1]. This diversity allows by different mechanisms to conduit several cations. They have similar chemical environments but they have different ion selectivity. Two of them (sites S3 and S4) are conserved, that is to say they are the same than in the high selective K+ channel while S1 and S2 become a vestibular structure where K+ and Na+ ions can diffuse [2].
Image:Biding sites.jpg
We will see for every binding site how his structure allows the passage of one or several ions.
Regulation
Structural highlights
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