Sandbox Reserved 1069: Difference between revisions

<scene name='69/694236/Binding_site_a/1'>Binding site A</scene> is in the <scene name='69/694236/Binding_site_a_transparent/1'>center</scene> of the transmembrane domain, attached and confined via residues from the TM2 and TM5 helices. The TM2 domain has <scene name='69/694236/Asp45/1'>Asp45</scene> and <scene name='69/694235/Asp49/1'>Asp49</scene>, and the TM5 has <scene name='69/694235/His153/1'>His153</scene> and <scene name='69/694235/Asp153/2'>Asp157</scene>, which facilitate the binding and releasing of Zn²⁺ within the sites. The TM5 helix is significantly shorter than the other 5 helices around it, and this length forms a cavity in the membrane. Site A is one of Yiip's active site, where Zn²⁺ is able to attach and eventually exit the cell via proton transport. This particular site has an ideal tetrahedron among its residues, which is preferred for Zn²⁺ binding.

It is important to note that the structure of this binding site is rigid because of the coordination of the Zn²⁺ between the four residues. This rigidity is indicative that any slight shift on either of the helices will cause a drastic readjustment of the coordination of Zn²⁺. In addition, there are no outer-shell constraints to hold the residues in place, which means that with a readjustment of the molecule, there is no energy being expended to bind or release another Zn²⁺ molecule. Therefore, the Zn²⁺ is able to rapidly release and a new Zn²⁺ can bind again with a simple reorientation or shift of the molecule. This rapid on/off bind and release mechanism is the regulator of homeostatic levels of Zn²⁺ in the cell, which is significantly faster than other Zn²⁺ exchange rate proteins by several orders of magnitude.