Lipid-protein interactions of immunoreceptor signaling subunit cytoplasmic domains

Abstract

Protein-lipid interactions are emerging as key components of cellular processes such as protein and membrane trafficking and cell-cell signaling. Many proteins bind lipid reversibly, including cytoplasmic proteins involved in signal transduction, such as Ras and Src. Membrane binding is vital for the function of these signaling proteins both through co-localization with other signaling proteins as well as effects of lipid on intrinsic activities. In this thesis, protein-lipid interactions of subunits of key antigen recognition receptors of the immune system are investigated. The proteins studied are the cytoplasmic domains of immunoreceptor signaling subunits that mediate transmembrane signal transduction in response to receptor engagement. The cytoplasmic domains derive from the T cell receptor, the B cell receptor, Fe receptors and Natural Killer cell stimulatory receptors. The TCR, CD3, CD3, CD3, ... and DAP12 cytoplasmic domains all bind lipid, whereas those of B cell receptor Iga and Igp do not. While all of these proteins are unstructured in solution, ... and CD3 undergo extensive increases in secondary structure upon lipid binding. Lipid binding of ... is found to inhibit its accessibility to kinase-mediated phosphorylation. Based on these results it is proposed that interactions with lipid may regulate the function of receptor cytoplasmic domains, as with many cytosolic proteins involved in signaling processes.