In my thesis, I’ll use PDZ domain as an example to illustrate how could a small modular domain achieves its specific and diverse binding property within two important molecules of the epithelial cell polarity system: ZO-1 and Par-3....[ Read more ]

In my thesis, I’ll use PDZ domain as an example to illustrate how could a small modular domain achieves its specific and diverse binding property within two important molecules of the epithelial cell polarity system: ZO-1 and Par-3.

ZO1 has long been considered as a passive scaffold protein and so is classified as a member of membrane associated guanylate kinase (MAGUK) family of proteins. I demonstrated that PDZ2 domain of ZO1 has a novel domain-swapped conformation that generates a specific regulatory binding site for Cx43. We proposed the regulatory mechanism from insights into the protein structure and proved this with cell biology results. I also performed the first biochemical and structural characterization of the conserved core MAGUK region (PDZ-SH3-Guk) in ZO1 and showed that the PDZ domain directly interacts with the SH3-GuK module to form an integral structural supramodule with distinct target binding properties with respect to the isolated domains. Based on structures in our studies we suggest that the PDZ-SH3-GuK tandems of other MAGUKs can also form supramodules.

In the meantime, I have also been involved in studying protein-protein interactions in the Par polarity complex (Par3/Par6/aPKC) and demonstrated that the PDZ2 domain of Par3 is a membrane-lipid binding module which is important for its proper polarized function in MDCK epithelial cells. I also found that around 15% of all human/mouse PDZ domains show this PDZ-lipid interaction. Following this work, I characterized the structure of PDZ1 Par3 and its association with cell adhesion molecules through its PDZ binding motif. I've also characterized the 100K isoform of Par-3 as being in an "auto-inhibited" conformation in Cos-7 and MDCK cell lines.