There is a fundamental gap in our understanding of how Enterotoxin LT-II binding to angliosides in the cell membrane modulates the structure and function (e.g. membrane-associated signaling) of the immune-cell membrane. It is necessary to address this gap in order to understand and further the use of these molecules as adjuvants to potentiate the cellular immune response. Such adjuvant reagents are essential components of vaccines. Our long-term goal is to understand the impact of changes in cell membrane ultra-structure on immune-cell membrane signaling at the molecular level. The objective of this proposal is to determine how the adjuvant Enterotoxin LT-II alters the membrane ultra-structure to influence membrane signaling. In particular, we aim to determine the effects of Enterotoxin binding on interactions between membrane proteins and cholesterol-dependent and -independent membrane domains, or nanoclusters. Based on preliminary data, our hypothesis is that adjuvant binding to gangliosides increases the stability of cholesterol-dependent nanoclusters, or the association of the receptor proteins with these clusters. The rationale for the proposed research is that a biophysical model of the influence of changes in membrane ultra-structure on cellular signaling will explain adjuvant potentiation of immune signaling. This hypothesis will be tested by quantifying the effects of Enterotoxin on the size, stability, and association of immune signaling proteins with lipid- and protein-membrane domains, and the membrane cytoskeleton;and by indentifying which membrane bound immune signaling processes are influenced by Enterotoxin binding. Our approach is extremely innovative and novel: We will establish advanced imaging methods which allow us to quantify membrane protein interaction with cholesterol-dependent and -independent nanoclusters and cytoskeleton continuously in intact cells. Our methods will enable a first real-time quantification of membrane structure modulation induced by enterotoxin binding. In addition, our study is uniquely suited to identify the relationship of changes in membrane structure to modulation of membrane function, e.g. cell signaling. By establishing this direct association between structural and functional changes in response to external perturbation will achieve an understanding of the role of the structure for function. The proposed research is significant because it will enhance our basic molecular understanding of the effect of enterotoxin like adjuvants, thus facilitating further investigation into optimizing the desired immune potentiating function. In addition, our results will expand the current understanding of the regulation of membrane structures such as lipid domains and the membrane cytoskeleton, and will elucidate their roles in natural immune function.
Experiments to reveal the molecular processes by which enterotoxin-like agents modulate membrane ultra-structure and the mechanisms by which these changes influence immune signaling will guide the design of future immune adjuvants, which will have direct relevance to issues of public health. The broader impact of this project will be an improved understanding of how agents that modulate membrane structure influence cell signaling. Thus, the proposed research is relevant to NIH's mission that pertains to developing fundamental knowledge to help to protect and improve human health.
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