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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 determines what. 3H90 is a crystal structure YiiP in its outward-facing conformation where Zn2+ is released from site A and H+ binds in its place. 3J1Z(a Yiip homolog derived from Shewanella oneidensis) has been crystallized using cryoelectron microscopy to show an inward facing conformation. In this conformation H+ releases from Site A and Zn2+ binds in its place. The energy for inducing the conformation change is postulated to come from the binding energy of each substrate. The binding of Zn2+ favors the outward-facing conformation and the binding of H+ favors the inward-facing conformation. The proton motive force provides the driving force to export Zn2+ from the cytoplasm.
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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