Protein export at the ER: loading big collagens into COPII carriers.

COPII vesicles mediate the export of secretory cargo from endoplasmic reticulum (ER) exit sites. However, of 60-90 nm diameter COPII vesicles are too small to accommodate secreted molecules such as the collagens. The ER exit site-located proteins TANGO1 and cTAGE5 are required for the transport of collagens and therefore provide a means to understand the export of big cargo and the mechanism of COPII carrier size regulation commensurate with cargo dimensions.