Abstract
Many signaling molecules involved in G protein-mediated signal transduction, which are present in the lipid rafts and believed to be controlled spatially and temporally, influence the potency and efficacy of neurotransmitter receptors and transporters. This has focus interest on lipid rafts and the notion that these microdomains acts as a kind of signaling platform and thus have an important role in the expression of membrane receptor-mediated signal transduction, cancer, immune responses, neurotransmission, viral infections and various other phenomena due to specific and efficient signaling according to extracellular stimuli. However, the real structure of lipid rafts has not been observed so far due to its small size and a lack of sufficiently sophisticated observation systems. A soft X-ray microscope using a coherent soft X-ray laser in the water window region (2.3–4.4 nm) should prove to be a most powerful tool to observe the dynamic structure of lipid rafts of several tens of nanometers in size in living cells. We have developed for the X-ray microscope a new compact soft X-ray laser using strongly induced plasma high harmonic resonance. We have also developed a time-resolved highly sensitive fluorescence resonance energy transfer (FRET) system and confirmed protein-protein interactions coupled with ligands. The simultaneous use of these new tools for observation of localization of G-protein coupled receptors (GPCRs) in rafts has become an important and optimum tool system to analyze the dynamics of signal transduction through rafts as signaling platform. New technology to visualize rafts is expected to lead to the understanding of those dynamics and innovative development of drug discovery that targets GPCRs localized in lipid rafts.
Highlights
Membrane or transmembrane receptors [1] are located at the cell membrane and play the very important role of signal transduction of the information from the outside into the cell
We show cases that have been reported for localization to lipid rafts in Table 1, especially in basic molecular groups involved in signaling through trimeric G protein
X-ray microscope is not limited to imaging of rafts and would have significant effects on the contributions to the field of transcription regulation which is the most important research in the post-genomic era
Summary
Membrane or transmembrane receptors [1] are located at the cell membrane and play the very important role of signal transduction of the information from the outside into the cell. It has become to be recognized that cell ultrastructures of a few tens of nanometers in size (microdomains), which cannot be observed with an optical microscope nor with an electron microscope under living conditions, play a very important functional role in the molecular mechanism of biological reactions [18]. Using the integrated technical development of the probe, which labels membrane proteins presented in a lipid raft structure, the development of novel therapies to elucidate the pathogenesis of cancer and lifestyle diseases and a detailed study of changes in quantitative and qualitative changes in signaling by molecular components of lipid rafts with aging and disease including even Alzheimer’s disease, mad cow disease and other emerging infectious virus diseases with aging and disease become a variety of useful information for the treatment or prevention of disease. We discuss in this review the simultaneous measurements of visualization of lipid rafts and dynamics of the localization of GPCRs in lipid rafts using our new soft X-ray laser technique of harmonic resonance and highly sensitive time-resolved FRET spectroscopy
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