Understanding the Functional Role of Protein Palmitoylation in Disease
Protein S-palmitoylation is an essential post-translational modification that regulates protein structure and function. It consists of the attachment of a palmitic acid to one or more cysteine residues through a thioester linkage. In cellular proteins, S-palmitoylation plays an important role in membrane localization, trafficking, lipid raft association, and cell signaling. Various viral proteins are also modified with S-palmitoylation; however, their functional role differs from that of cellular proteins. One of the main differences is that S-palmitoylation is a reversible process in cellular proteins, which allows for recycling and regulation of protein function, whereas in viral proteins, there is no functional benefit to recycle and reuse proteins after viral entry and infection has occurred. The unique nature of S-palmitoylation on protein function makes it an interesting lipid post-translational modification to further characterize and potentially target for therapeutic purposes. There are not many studies that have focused on S-palmitoylation as a targeted therapeutic approach, which makes it even more intriguing to fully understand its effects on cellular and viral proteins. In this dissertation, I examined the effects of directly targeting S-palmitoylation of the NRAS protein, which is highly mutated in multiple cancers including melanoma, using a novel amphiphile-mediated depalmitoylation approach. I discovered that this chemoselective strategy causes delocalization of NRAS from the plasma membrane, inhibition of downstream oncogenic signaling pathways in NRAS-mutated melanoma cells, and reduction of tumor growth in NRAS-mutated melanoma xenograft mice. Additionally, I focused on understanding the role of S-palmitoylation on the SARS-CoV-2 spike glycoprotein. I determined the essential sites of palmitoylation within the C-terminal cysteine-rich region as well as the palmitoylation-dependence of membrane fusion between the spike protein and the host ACE2 receptor. Taken together, these studies highlight the significance of S-palmitoylation on cellular proteins, such as the effect on NRAS function and downstream signaling, and viral proteins, specifically the role on SARS-CoV-2 spike protein-mediated virus-cell membrane fusion, that are involved in various diseases.