The pathway of collagen secretion

V Malhotra, P Erlmann - Annual review of cell and …, 2015 - annualreviews.org
Annual review of cell and developmental biology, 2015annualreviews.org
COPII vesicles mediate export of secretory cargo from the endoplasmic reticulum (ER).
However, a standard COPII vesicle with a diameter of 60–90 nm is too small to export
collagens that are composed of rigid triple helices of up to 400 nm in length. How do cells
pack and secrete such bulky molecules? This issue is fundamentally important, as collagens
constitute approximately 25% of our dry body weight and are essential for almost all cell-cell
interactions. Recently, a potential mechanism for the biogenesis of mega-transport carriers …
COPII vesicles mediate export of secretory cargo from the endoplasmic reticulum (ER). However, a standard COPII vesicle with a diameter of 60–90 nm is too small to export collagens that are composed of rigid triple helices of up to 400 nm in length. How do cells pack and secrete such bulky molecules? This issue is fundamentally important, as collagens constitute approximately 25% of our dry body weight and are essential for almost all cell-cell interactions. Recently, a potential mechanism for the biogenesis of mega-transport carriers was identified, involving packing collagens and increasing the size of COPII coats. Packing is mediated by TANGO1, which binds procollagen VII in the lumen and interacts with the COPII proteins Sec23/Sec24 on the cytoplasmic side of the ER. Cullin3, an E3 ligase, and its specific adaptor protein, KLHL12, ubiquitinate Sec31, which could increase the size of COPII coats. Recruitment of these proteins and their specific interactors into COPII-mediated vesicle biogenesis may be all that is needed for the export of bulky collagens from the ER. Nonetheless, we present an alternative pathway in which TANGO1 and COPII cooperate to export collagens without generating a mega-transport carrier.
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