Dynamic composition of membrane microdomains

Lipid rafts are cholesterol enriched membrane microdomains involved in many cellular functions. Caveolae are a sub-type of lipid rafts that are smooth invaginations of the plasma membrane (PM) whose formation requires caveolin-1 (Cav1). Here, we determined the lipid rafts and caveolae proteome from various cells in an unbiased manner and examined the dynamic raft proteome change during Salmonella infection using quantitative proteomics. In chapter 2, we approach the status of mitochondrial proteins in detergent-resistant membrane (DRM) preparations by employing Stable Isotope Labeling by Amino acids in Cell culture (SILAC) to evaluate the composition of differentially purified subcellular fractions. Our data demonstrate that mitochondrial proteins that were previously identified as raft components are partially co-purifying contaminants of raft preparations. In tumor cells deficient for Golgi β-1,6N-acetylglucosaminyltransferase V (Mgat5), reduced Cav1 expression is associated not with caveolae but with oligomerized Cav1 domains, or scaffolds. These cell lines displaying differing Cav1/caveolae phenotypes are effective tools for probing the composition of caveolae. Using SILAC in chapter 3, we are able to quantitatively distinguish the composition of caveolae from the background of DRM proteins and show that the presence of caveolae enriches protein composition of DRM, including the recruitment of multiple heterotrimeric G-protein subunits. Furthermore in chapter 4, we explored the dynamic change of membrane protein composition according to an external signal. Salmonella are Gram-negative intracellular bacteria believed to attack lipid rafts as the site of entry. We applied SILAC examined the change of host raft proteome at a couple of time points during Salmonella infection. Dozens of proteins have shown to be highly regulated, one of them – Cav1 is shown to be required by Salmonella entrance. We also developed a high-content screening assay that is able to estimate the number of bacteria entered or survived inside the host for future functional studies of the novel proteins identified. This research gives us a better understanding of the raft proteome and how rafts are localized, as well as it can be changed. The Salmonella infection work leads to a global raft proteome dynamic analysis and identifies several proteins that may be novel bacterial host targets.Medicine, Faculty ofBiochemistry and Molecular Biology, Department ofGraduat