Information processing on the membrane microdomain, "raft"

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In order to understand the molecular signal transduction mechanism in the mammalian central nervous system, I have performed the characterization of the molecular components in the membrane microdomain "raft" and obtained following results.1. The molecular function of NAP-22, a major component of neuronal raft, was elucidated to assemble cholesterol within the membrane. Calmodulin inhibited this function in aCa^<2+>- dependent manner. The cholesterol binding ability was observed in the presence of phosphatidylcholine and the induction of the assembly of cholesterol was observed not only in a liposome assay system but also in NAP-22 expressed cultured cells.2. The time course of the localization of NAP-22 on the axonal region was assayed to estimate the contribution of NAP-22 in the cell polarization process. The localization was clearly observed after the establishment of the cell polarity. This result suggests that NAP-22 participate in the maintenance rather than the establishment of the cell polarity.3. The localization of Rac1, but not Cdc42 nor Rho, in the raft was observed. The participation of these low molecular G proteins in the cell morphological changes is well known. This result indicates that there is spatial localization of these morphology-affecting proteins within the cell membrane.4. The characterization of the raft components in the chromaffin granule membrane from bovine adrenal medulla revealed the predominant localization of H+-ATPase in the raft. This result indicates an important role of raft in the membrane cycling process.5. Total characterization of GPI-anchored proteins in the raft fraction resulted the identification of a novel protein Kilon. The localization of kilon in the synaptic region in the central nervous system was studied using immunohistochemical methods.