Collagen export from the endoplasmic reticulum (ER) requires TANGO1, COPII coats, and retrograde fusion of ERGIC membranes. How do these components come together to produce a transport carrier commensurate with the bulky cargo collagen? TANGO1 is known to form a ring that corrals COPII coats, and we show here how this ring or fence is assembled. Our data reveal that a TANGO1 ring is organized by its radial interaction with COPII, and lateral interactions with cTAGE5, TANGO1-short or itself. Of particular interest is the finding that TANGO1 recruits ERGIC membranes for collagen export via the NRZ (NBAS/RINT1/ZW10) tether complex. Therefore, TANGO1 couples retrograde membrane flow to anterograde cargo transport. Without the NRZ complex, the TANGO1 ring does not assemble, suggesting its role in nucleating or stabilising this process. Thus, coordinated capture of COPII coats, cTAGE5, TANGO1-short, and tethers by TANGO1 assembles a collagen export machine at the ER.

V Malhotra is an Institució Catalana de Recerca i Estudis Avançats professor at the Centre for Genomic Regulation, the work in his laboratory is funded by grants from the Ministerio de Economía, Industria y Competitividad Plan Nacional (ref. BFU2013-44188-P) and Consolider (CSD2009-00016). We acknowledge support of the Spanish Ministry of Economy and Competitiveness, through the Programmes ‘Centro de Excelencia Severo Ochoa 2013–2017’ (SEV-2012–0208) and Maria de Maeztu Units of Excellence in R and D (MDM-2015–0502). We acknowledge the support of the CERCA Programme/Generalitat de Catalunya. F Campelo and M García-Parajo acknowledge support by the Spanish Ministry of Economy and Competitiveness (‘Severo Ochoa’ Programme for Centres of Excellence in R and D (SEV-2015–240522) and FIS2014-56107-R), BFU2015-73288-JIN, AEI/FEDER; UE, Fundacion Privada Cellex, HFSP (GA RGP0027/2012), EC FP7-NANO-VISTA (GA 288263) and LaserLab 4 Europe (GA 654148). I. Raote and F. Campelo acknowledge support by the BIST Ignite Grant (eTANGO).