Sandbox Reserved 1066: Difference between revisions

YiiP's ability to export Zn²⁺ from the cytoplasm is best described as an alternating access mechanism with Zn²⁺/H⁺ antiport. YiiP has 2 major structural conformations which is supported by the crystallized structures 3H90 and 3J1Z (a YiiP homolog derived from Shewanella oneidensis). 3H90 shows YiiP in its outward-facing conformation and 3J1Z shows the YiiP homolog in an inward-facing conformation.

Conformation changes occur in the TMD and CTD, both of which are heavily influenced by the presence of Zn²⁺.Both of these conformation changes  

The conformation change directly involved with Zn²⁺/H⁺ antiport occurs in the TMD as helix pivoting controls what environment site A is available to. Conformation change occurs when the transmembrane helix pairs TM3-TM6 pivot around cation binding site. It is believed that the energy for TMD conformation change comes from energy of binding each substrate. Changing to the outward from the inward-facing conformation causes a shift in TM5 which disrupts the tetrahedral geometry of active site A. This in turn decreases binding affinity site A has for Zn²⁺ and causes Zn²⁺ to leave which then favors change back to inward-facing conformation.

In contrast the main purpose of conformation change in the CTD is to stabilize the YiiP dimer and act a Zn²⁺ sensor. Using FRET to measure the distance between the CTD of each monomer showed fluorescence quenching as the concentration Zn²⁺ increased. It is not probable that Zn²⁺ bound at site C works it way up to sites A or B, as C binds Zn²⁺ with a much greater affinity.