[1P-56*] サポシンタンパク質によるCD1bへの脂質積込みの機能解析
CD1b is one of glycoproteins expressed on surfaces of various antigen-presenting cells. CD1b is related to Major Histocompatibility Complex (MHC) class I molecules, and is involved in the presentation of lipid and lipid-based molecules to activate T cells. CD1b can bind and present varieties of lipidic ligands during the endocytic pathway. However, the nonpolar nature of lipids extracted from the membranes have unfavorable feature to mobilize across the aqueous endocytic environment, and they need the assistant of molecular mediators such as Saposin proteins. In this presentation, we report the interaction analysis between CD1b and Saposin proteins. Human CD1b ectodomain was prepared using the silkworm-baculovirus expression system. Saposin A, B, C and D were expressed in E.coli based on the published paper. With the lipidic detergent, Saposin C proteins tend to form oligomer at acidic pH evaluating by size exclusion chromatography. To reveal the mechanism how Saposin proteins transfer lipids to CD1b, pull down assay experiment and surface plasmon resonance experiment were conducted. The result showed that on the lysosomal pH (pH 4.8) the binding of CD1b toward Saposin C seems to be mediated by electrostatic interactions.