Cell
Volume 143, Issue 5, 24 November 2010, Pages 774-788
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Article
Mechanisms Determining the Morphology of the Peripheral ER

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Summary

The endoplasmic reticulum (ER) consists of the nuclear envelope and a peripheral network of tubules and membrane sheets. The tubules are shaped by the curvature-stabilizing proteins reticulons and DP1/Yop1p, but how the sheets are formed is unclear. Here, we identify several sheet-enriched membrane proteins in the mammalian ER, including proteins that translocate and modify newly synthesized polypeptides, as well as coiled-coil membrane proteins that are highly upregulated in cells with proliferated ER sheets, all of which are localized by membrane-bound polysomes. These results indicate that sheets and tubules correspond to rough and smooth ER, respectively. One of the coiled-coil proteins, Climp63, serves as a “luminal ER spacer” and forms sheets when overexpressed. More universally, however, sheet formation appears to involve the reticulons and DP1/Yop1p, which localize to sheet edges and whose abundance determines the ratio of sheets to tubules. These proteins may generate sheets by stabilizing the high curvature of edges.

Highlights

► ER sheets are formed by edge stabilization through curvature-generating proteins ► Climp63 regulates the area and luminal width of ER sheets in mammalian cells ► ER sheets are enriched in translocon components and functionally signify rough ER ► Membrane-bound polysomes concentrate rough ER proteins to sheets

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