Structure Of Zinc Ion Transporter ZnT3 And Its Potential Application In Children With Febrile Epilepsy

Zn²⁺is the second most essential trace element in the human body,and its homeostasis is crucial for maintaining vital biological functions.In the mossy fibers of the hippocampus,Zn²⁺is mainly transported into synaptic vesicles through the zinc transporter protein ZnT3.The hippocampus is an area in the brain involved in learning and memory.Deficiency of ZnT3 leads to dysregulation of zinc homeostasis in the brain and is believed to be closely associated with the development of neurological disorders such as Parkinson’s disease and febrile seizures.Studies on mice in epileptic states have shown an upregulation of ZnT3 protein expression.Therefore,ZnT3 may become a new target for treating such neurological disorders.Understanding the structure of ZnT3 and the conformational changes during zinc ion transport provides valuable insights for the treatment of these neurological disorders.Recently,the cryo-electron microscopy structure of human ZnT8 at a resolution of4.1（?）revealed an open conformation facing the lumen when binding zinc ions.In this study,we purified human ZnT3 protein under cytoplasmic p H 7.6 conditions and obtained a conformation of ZnT3 facing the cytoplasm when binding zinc ions（resolution of 3.14（?））.This contributes to a deeper understanding of the mechanism of proton-driven zinc ion transport in the Zn T family.However,under luminal p H 6.0 conditions,we did not obtain a conformation facing the lumen.By comparing with the outward-facing conformation of ZnT8,the conformational changes in zinc ion transport by the Zn T family can be inferred:the transmembrane helices（TMH3 and TMH6）together with the C-terminal domain（CTD）participate in dimerization.During the transition from the cytoplasm-facing open state to the lumen-facing open state,TMH1 and TMH2 pivot towards the cytoplasm,while TMH4 and TMH5 pivot towards the lumen,completing the entire transport process.It has been found that a high-fat,low-carbohydrate ketogenic diet has therapeutic effects on drug-resistant epilepsy,and there may be certain associations between zinc metabolism and lipid metabolism.We discovered a density that potentially corresponds to phosphatidylglycerol in the structural density map and conducted cell-based zinc ion transport activity experiments to validate the possible influence of arginine at position 286near phosphatidylglycerol on ZnT3 transport activity.Further research is needed to elucidate the role of phosphatidylglycerol in ZnT3.In conclusion,this study provides structural insights into the zinc ion transport mechanism of the Zn T family and lays the foundation for virtual screening of small molecule drugs.