Current Research

Hu laboratory has broad interest in structural biology of membrane proteins and biomolecules involved in metal homeostasis. By applying multidisciplinary approaches, including X-ray crystallography, NMR and other biochemical/biophysical/cell biological methods, we are aiming to clarify the detailed molecular mechanism of how the complicated biological system works at atomic level. Currently, we have two major projects and several collaborative projects ongoing.

 

Zinc Transporter - ZIP family. Zirt-Irt like protein (ZIP) family consists of a group of integral membrane proteins playing crucial roles in zinc and iron transport across cell membrane. In human, the fourteen ZIPs are involved in a variety of biological processes and linked with human diseases. Our current research is focused on ZIP4, a representative member in the mammalian ZIP family. ZIP4 is exclusively responsible for zinc uptake from intestine and ZIP4 mutations lead to a lethal genetic disorder, Acrodermatitis enteropathica (AE). ZIP4 is upregulated on several types of cancer, particularly in pancreatic cancer cells, making ZIP4 potential drug target for cancers. In this project, our aims include: (1) Solve the crystal structure of ZIP4; (2) Elucidate zinc transport mechanism; and (3) Clarify the molecular mechanism of zinc-induced ZIP4 endocytosis. This work will also provide a structural framework for rational drug design against pancreatic cancer and other relevant diseases (Figure 1).

ZIP4 model
Figure 1. Topology of ZIP4. The extracellular domain of ZIP4 is shown in cartoon mode (PDB: 4X82).

 

Lipid Kinases - PIPK family. Phosphatidylinositol phosphate kinase (PIPK) family consists of central players in the metabolism of phosphoinositides (e.g., PIP2), which are crucial signaling molecules in numerous biological processes. PIPKs are also potential drug targets for human diseases, including cancers, diabetes, inflammations and chronic pain. The aim of our research is to establish the catalytic mechanism of the interfacial reaction, the molecular mechanism of substrate specificity, and particularly, the regulation mechanism by their binding partners and lipid molecules. We are also interested in structure-based drug design (Figure 2).

Activation loop model
Figure 2. Activation loop (cyan) acts as a membrane sensor regulating the function of PIPKs. The catalytic residue is shown in red.

 

Collaborative projects:

Lar proteins. LarA is a nickel-dependent racemase which catalyzes the inversion of the stereochemistry of lactic acid. The activity of LarA absolutely depends on a newly-discovered cofactor which is biosynthesized by LarB, LarC and LarE. We are working with Dr. Robert Hausinger at MMG to (1) clarify the catalytic mechanism of LarA; and (2) establish the biosynthesis pathway of this novel Ni(II) pincer cofactor by other Lar proteins (Figure 3).

LarAlr model
Figure 3. Crystal structure of LarALR and the Ni(II)-containing catalytic center (right). The Ni(II) pincer complex, composed of the organic compound PTTMN and a bound NI(II), is a novel cofactor. (PDB: 5HUQ).

 

Calcium Sensing Receptor. Calcium sensing receptor (CaSR) is a G protein-coupled receptor (GPCR) and a vital player in calcium homeostasis in human. Through collaboration with Dr. Jenny Yang (Georgia State University) and Dr. Edward Brown (Harvard University), we are conducting structural biology studies on CaSR, particularly on the extracellular domain (ECD) where metals/ligands bind and many disease-causing mutations occur. Our goal is to establish a structural framework for better understanding the activation mechanism by natural ligands, which is crucial for the design of agonist and antagonist of CaSR for human diseases (Figure 4).

calcium sensing receptor model
Figure 4. Crystal structure of the extracellular domain of human Calcium Sensing Receptor (PDB: 5FBK and 5FBH).