COLL 536

Affiliation: Cornell University, Ithaca, NY

The complex role of plasma membrane structure in orchestrating receptor-mediated signal transduction is addressed in collaborative studies investigating how antigen crosslinking of IgE-receptors on mast cells initiates signaling pathways leading to multiple cellular responses. Segregation of liquid ordered regions from disordered regions of the plasma membrane provides protection from transmembrane phosphatases and thereby a mechanism for crosslinking-dependent phosphorylation of IgE-receptors by active Lyn kinase. Fluorescence correlation spectroscopy reveals that antigen crosslinking reduces the diffusion of receptors and also Lyn, with temporally resolved interactions occurring between these two components. Defined clustering of IgE-receptors on the micron scale with patterned lipid bilayers enables visualization of interacting components with spatial and temporal resolution. With total internal reflection fluorescence microscopy we find that stimulated exocytosis of secretory granules and recycling endosomes are targeted differently with respect to the clustered receptors. Electron spin resonance allows the phase behavior of plasma membranes to be examined in purified preparations and living cells and reveals distinct ordered and disordered regions. Giant plasma membrane vesicles uncoupled from the cytoskeleton, undergo large scale phase separation and can be used to investigate partitioning of lipids and proteins between coexisting fluid phases. This provides a new approach for investigating membrane structural heterogeneity.