ER arrival sites for COPI vesicles localize to hotspots of membrane trafficking

Abstract

COPI-coated vesicles mediate retrograde membrane traffic from the cis-Golgi to the endoplasmic reticulum (ER) in all eukaryotic cells. However, it is still unknown whether COPI vesicles fuse everywhere or at specific sites with the ER membrane. Taking advantage of the circumstance that the vesicles still carry their coat when they arrive at the ER, we have visualized active ER arrival sites (ERAS) by monitoring contact between COPI coat components and the ER-resident Dsl tethering complex using bimolecular fluorescence complementation (BiFC). ERAS form punctate structures near Golgi compartments, clearly distinct from ER exit sites. Furthermore, ERAS are highly polarized in an actin and myosin V-dependent manner and are localized near hotspots of plasma membrane expansion. Genetic experiments suggest that the COPI•Dsl BiFC complexes recapitulate the physiological interaction between COPI and the Dsl complex and that COPI vesicles are mistargeted in dsl1 mutants. We conclude that the Dsl complex functions in confining COPI vesicle fusion sites.

TANGO1 builds a machine for collagen export by recruiting and spatially organizing COPII, tethers and membranes

“…A prime candidate for this tethering activity is the evolutionarily conserved NRZ ( N BAS, R INT1, Z W10) protein tether. NRZ tether is a multi-subunit tether complex (MTC) that assembles at the surface of the ER ( Ren et al, 2009 ), is required for retrograde capture of membranes ( Aoki et al, 2009 ; Arasaki et al, 2006 ; Hirose et al, 2004 ), partially localises to ER exit sites ( Schröter et al, 2016 ) and interacts with SNAREs that we have shown previously are required for collagen export from the ER ( Nogueira et al, 2014 ; Santos et al, 2015 ). One component of the MTC (RINT1) was also identified in our screen for genes required for protein secretion ( Bard et al, 2006 ).…”

Golgi trafficking defects in postnatal microcephaly: The evidence for “Golgipathies”

“…There is good evidence that RAB18 can bind the ER-resident Dsl1 protein complex (Gillingham et al, 2014), which tethers and fuses vesicles returning from the Golgi. This suggests that RAB18 may participate in the tethering of COPIcoated vesicles to the ER (Gillingham et al, 2014;Schroter et al, 2016). Interestingly, RAB18…”

Maintaining order: COG complex controls Golgi trafficking, processing, and sorting

“…This COG-COPI interaction may then stimulate COG-SNARE and COG-SM interactions, which in turn promote SNARE formation and vesicle fusion. In support to these predictions, another tether, the ER-localized Dsl1 complex, can bind to COPI, suggesting functional significance for this conserved tether/coat interaction [13,[147][148][149]. Alternatively, the initial Rab-COG membrane association could change the conformation of flexible 'arms' of COG subunits, allowing them to establish interactions with CCTs, SNAREs, and SM proteins leading to productive vesicle tethering and fusion.…”