Date of Award
Doctor of Philosophy (PhD)
Protein S-palmitoylation is a reversible post-translational lipid modification that regulates the trafficking, stability, and activity of proteins in eukaryotes. The detection of fatty-acylated proteins has been challenging but recent advances in chemical labeling methods have enabled more sensitive detection and proteomic analyses, which I summarize in Chapter 1. The proteomic analysis of S-palmitoylated proteins in dendritic cells and macrophages by our laboratory revealed that the interferon-induced transmembrane proteins (IFITMs) are S-fatty-acylated at conserved cysteine (Cys) residues. IFITMs are unique interferon-induced proteins that restrict the infection of multiple pathogenic viruses. Initial studies by our laboratory showed that S-fatty-acylation on three conserved Cys residues were crucial for IFITM3 anti-influenza virus activity. However, endogenous levels and site-specific functions of S-palmitoylation on the individual IFITM3 Cys residues were unknown and are addressed in Chapter 2. In collaboration with other members of the Hang laboratory, we discovered that endogenous IFITM3 is fully S-fatty-acylated in IFN-stimulated mammalian cells and that Cys72 in particular plays an important role in IFITM3 antiviral activity. My additional biochemical studies suggest S-palmitoylation may regulate IFITM3 protein turnover in mammalian cells. IFITMs appear to inhibit virus entry into mammalian cells, but the precise mechanisms have been unclear due to limited methods for live-cell imaging and IFITM3 protein-protein interaction studies. To address these limitations, I explored amber codon suppression technology for site-specific IFITM3 labeling with unnatural amino acids for bioorthogonal imaging and covalent protein crosslinking in mammalian cells in Chapter 3. Using the pyrrolysyl-tRNA synthetase (PylRS)/Pyl tRNACUA system, I showed that unnatural amino acid can be site-specifically incorporated throughout IFITM3 in mammalian cells. The site-specific labeling of IFITM3 with unnatural amino acids has provided new opportunities for live-cell imaging and photocrosslinking studies with specific interacting proteins in Chapter 4. My thesis studies have revealed additional insight into IFITM3 regulation by S-palmitoylation and established new tools to explore the antiviral mechanism of IFITMs.
Yuan, Xiaoqiu, "Chemical Tools for Exploring IFITM3 S-Palmitoylation and Mechanism" (2016). Student Theses and Dissertations. 307.