Presenting Author
Baylor College of Medicine
I'm a recent Ph.D. graduate in biochemistry from Baylor College of Medicine. I'm currently looking for a postdoctoral position in the field of metalloprotein. My graduate research is focused on the structural and functional studies of membrane-bound metalloenzymes and transporters through various biochemical and biophysical techniques, including X-ray crystallography, cryo-electron microscopy (cryo-EM), electron paramagnetic resonance (EPR) spectroscopy, rapid quench-flow, fluorescence- or radioligand-based transport in liposome, etc. I have received comprehensive training in the expression, purification, and characterization of challenging mammalian membrane proteins, and have successfully solved multiple structures, developed functional assays, and discovered novel mechanisms in these proteins. In addition, I have a good track record in performing collaborative research with scientists from different disciplines, including redox biochemistry, medicinal chemistry, etc. My major scientific contributions are as follows:
1. Crystal structures and biochemical & spectroscopic analyses advanced our understanding of the mechanism of a novel diiron center in mammalian stearoyl-CoA desaturase 1 (SCD1) and the interplay with its redox partners. We have overcome the issue of zinc misincorporation and obtained a large amount of diiron-containing SCD1, enabling structural and functional studies. We solved the structure of SCD1 with a unique diiron center different from those in soluble proteins, and discovered that SCD1 quickly loses activity (within ten turnovers) by losing one of the irons during reaction cycles. This irreversible deactivation can be prevented by external supply of Fe2+ prior to reaction. Using the assay with enhanced SCD1 activity, we have collaborated with an academic lab and a company to assess inhibitors against SCD1 developed for cancer and Parkinson's disease. Using the purified SCD1, we discovered multiple distinct EPR features from the diiron center, showing a stable metal-centered radical. Redox cycling monitored by EPR shows concerted changes of those features. The EPR spectrum from an iron-binding site mutant helps to identify the potential iron lost after reaction. Moreover, we demonstrated that SCD1, can form stable binary and ternary complexes with its redox partners, cyt b5, and b5R, via interactions in the membrane, which facilitate their redox communications on their soluble domains.
2. Cryo-EM structures and functional studies revealed mechanisms of iron transport and inhibition in mammalian ferroportin (Fpn, slc40a1). Fpn, as the only known iron exporter, is essential for iron homeostasis in human. By solving its structure, we identified two previously unknown iron-binding sites (S1 and S2). Metal transport assays demonstrate that the Fe2+ transport is coupled to H+ antiport in an electroneutral manner. In addition, we have shown that Ca2+ can bind and be transported by Fpn, and visualized the Ca2+ binding site that shares a residue from S1. The competitive binding of Ca2+ against Fe2+ implies the regulatory role of Ca2+ in iron transport. We also solved the structure of Fpn bound to a high-affinity inhibitor, PR73, developed based on a hormone hepcidin that regulates Fpn activity in vivo. We found that the PR73 can form a disulfide bridge with the Cys from S2, which is not observed in the hepcidin binding.
3. Cryo-EM structure of a mammalian peptide transporter (PepT, slc15) revealed a potential structural determinant that differentiates PepT1 and PepT2. PepT1 mediates proton-coupled peptide transport, which has been exploited for drug and prodrugs uptake. From the structure of an inward-facing mammalian PepT1, we discovered a novel extracellular gate formed between the extracellular domain (ECD, ~20 kDa) and TM1 of the transporter, which is only conserved in PepT1 but not in PepT2. We validated its indispensable role in the transport activity of PepT1. Our findings reveal a new role of ECD and may help to understand how PepT1 and PepT2 have evolved to possess different transport properties.