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DP1/Yop1p is an integral membrane protein family that, along with the reticulons, is responsible for the shape of the tubular endoplasmic reticulum (ER) in yeast and mammalian cells. Furthermore, it is also believed that they might be involved in sheet ER formation.〔Mechanisms Determining the Morphology of the Peripherial ER〕 About half the total area of membrane in an eukaryotic cell encloses the space of the endoplasmic reticulum. The ER is an extremely dynamic membrane organelle which consists of the nuclear envelope and the peripheral ER. It is organized into a netlike labyrinth of branching tubules and flattened sheets that extends throughout the cytosol. These tubules and sheets are interconnected and their membrane is continuous with the outer nuclear membrane. The ER and nuclear membranes form a continuous layer enclosing a single internal space, called the ER lumen, which often occupies the 10% of the total cell volume.〔Molecular Biology of the Cell〕 However, this unique space has several morphologically distinct areas.〔How the ER Stays in Shape〕 Thus, the peripheral ER is composed of a polygonal network of tubules and interdispersed sheets that spreads from the nuclear envelope to the cell cortex. At an ultrastructural level, the ER can be classified into two types, rough ER (RER) and smooth ER (SER). The RER has a sheet-like morphology and its main feature is the presence of ribosomes. Conversely, the SER is devoid of ribosomes and tends to be more tubular in structure. The peripheral ER is dynamic: the tubules continuously form and disappear and the sheets rearrange.〔ER structure and function〕 ER shaping proteins (reticulons and Dp1/Yop1p) play key roles in generating and maintaning this unique reticular morphology of the ER. An intact peripheral ER is functionally important in higher eukaryotes. Failure to maintain this structure could be related to certain neurological disorders. In all eukaryotic cells, the ER plays an important role in decisive processes, such as the biosynthesis of secretory and membrane proteins, protein modification, lipid synthesis and calcium storage (used in many cell signaling responses). Both mammalian DP1 (for “deleted in polyposis”) and Yop1p in yeast cells are ubiquitously expressed and found in most eukaryotic cells. They are predominantly localized to the tubular ER and to the highly curved edges of ER sheets. ==Function== DP1/Yop1p proteins play an important role in the morphology of the ER as they are one of the major components that determine and maintain the shape of ER tubules, which are long cylindrical units with high membrane curvature in their cross-section and a diameter that usually fluctuates between 60 and 100 nm. Both the reticulons and DP1/Yop1p are tethered to the cytoskeleton and diffuse slowly in the ER membrane, probably due to the fact that they form oligomers.〔The Reticulon and Dp1/Yop1p Proteins Form Immobile Oligomers in the Tubular Endoplasmic Reticulum〕 The structural regularity of the different units that form the ER indicates that tubules are shaped actively. It is believed that DP1/Yop1p proteins may stabilize the high curvature of ER tubules by “wedging” themselves into the outer membrane leaflet, creating the necessary increase in local surface area and membrane asymmetry 〔Mechanisms shaping cell membranes〕 needed for high membrane curvature 〔Rough Sheets and Smooth Tubules〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Yop1p」の詳細全文を読む スポンサード リンク
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