Sandbox Reserved 1066

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Organism

This protein is found in E. coli

Structure

YiiP is a homodimer with transmembrane (TMD) and C-terminal (CTD) domains that are connected via a charge interlocking mechanism located on a flexible loop. There are 3 Zn²⁺ binding sites per unit of homodimer. Site A is located in the TMD, site C is located in the CTD, and site B is located at the junction of the domains join. Both TMD are composed of 6 helices, 4 of which (TM1,TM2,TM4,TM5) form a pore in which Zn²⁺ and H⁺ can reach binding Site A. Zn²⁺ binding at site C helps hold the CTD together and is thought to stabilize conformational changes in YiiP.

Mechanism of Transport

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. The energy for inducing the conformation change from inward to outward is postulated to come from the binding energy of each substrate. The binding of Zn²⁺ favors the outward-facing conformation, but the outward facing conformation does not favor the binding of Zn²⁺. The same is observed with the inward-facing conformation and H⁺. Although YiiP exists as a homodimer both monomers can undergo conformation change independent of one other to produce the alternating access mechanism. The main driving force behind exporting Zn²⁺ from the cytoplasm is the proton motive force.

Zn Induced Conformation Change

Allosteric Inhibition

Zn binding to Active Site C causes a conformation change that reduces the affinity for Zn at Active Site A.

Structural highlights

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