Lipid Rafts and Signal Transduction by MHC Class II Molecules

Colorado State University, Fort Collins CO

Investigators

Abstract

The goal of this project is to explore interactions of lipid rafts, discrete small regions of the cell membrane having unique lipid compositions, with an important class of proteins, called Major Histocompatibility Complex (MHC) class II molecules, on the surfaces of B lymphocytes, a type of white blood cell. Lipid rafts are believed to be the sites where membrane proteins transmit information concerning extracellular conditions across the cell surface to initiate intracellular responses. MHC class II molecules help regulate B cell responses to T cells and to foreign antigenic peptides. The specific objectives are 1) to examine where and when specific class II molecules associate with lipid rafts and how this association relates to the number and type of class II molecules on the cell and 2) to assess how class II structural mutations and treatment with peptides and/or crosslinking reagents affect raft association. These studies will employ innovative optical measurements allowing protein-raft association to be evaluated on intact cells, including fluorescence energy transfer from labeled proteins to raft lipids and cholera toxin perturbation of protein rotation, as supported by density gradient centrifugation analysis of membrane lysates. The raft hypothesis, namely that lipid rafts are a key site for signal transduction events, is becoming a major paradigm in cell biology. However, most studies in this area have been performed by biochemical methods on disrupted cells. This project will employ optical approaches to evaluate the nature of raft-protein interactions on living cell surfaces. Thus the results will have wide implication for understanding how cells of all types, not just those to be examined in the project, respond to environmental factors. To promote teaching, training and learning, two graduate students will be key participants in the proposed project and the biophysical techniques to be refined during the project will contribute to research infrastructure of the biological sciences generally. Work will be conducted in collaboration with investigators at Dartmouth College which will facilitate disseminating modern science between researchers in diverse fields.