Cargo Can Modulate COPII Vesicle Formation from the Endoplasmic Reticulum

Abstract

The COPII coat complex found on endoplasmic reticulum (ER)-derived vesicles plays a critical role in cargo selection. We now address the potential role of biosynthetic cargo in modulating COPII coat assembly and vesicle budding. The ER accumulation of vesicular stomatitis glycoprotein (VSV-G), a transmembrane protein, or the soluble PiZ variant of ␣1-antitrypsin, reduced levels of general COPII vesicle formation in vivo. Consistent with this result, conditions that prevent the export of VSV-G from the ER led to a significant inhibition of general COPII vesicle budding from ER microsomes and the export of an endogenous recycling protein p58 in vitro. In contrast, synchronized export of VSV-G stimulated COPII vesicle budding both in vivo and in vitro. Under conditions where VSV-G is retained in the ER, we find that it can to be recovered in pre-budding complexes containing COPII components. These results suggest that the export of biosynthetic cargo is integrated with ER functions involved in protein folding and oligomerization. The ability of biosynthetic cargo to prevent or enhance ER export suggests that interactions of cargo with the COPII machinery contribute to the formation of vesicles budding from the ER.

The Cargo Receptors Surf4, Endoplasmic Reticulum-Golgi Intermediate Compartment (ERGIC)-53, and p25 Are Required to Maintain the Architecture of ERGIC and Golgi

“…ER export activity is known to be modulated by the cargo load (Aridor et al, 1999;Guo and Linstedt, 2006). Accordingly, the depletion of cargo receptors may impair ER export that would explain the reduction in ERGIC cluster numbers.…”

“…The reduction of KDEL-receptor-positive ERGIC structures was not due to reduced levels of KDEL-receptor (Supplemental Figure S3C). Clearly, both the Surf4/ERGIC-53 knockdown and the p25 knockdown reduced the number of peripheral ERGIC clusters.ER export activity is known to be modulated by the cargo load (Aridor et al, 1999;Guo and Linstedt, 2006). Accordingly, the depletion of cargo receptors may impair ER export that would explain the reduction in ERGIC cluster numbers.…”

Molecular evolution of the vesicle coat component βCOP in Toxoplasma gondii

“…In contrast to COPI, COPII's role in transport is well understood. It is required for the concentration and export of secretory cargo from the ER (Aridor et al, 1999;Barlowe, 1998;Barlowe, 2000;Gorelick and Shugrue, 2001;Gurkan et al, 2006). COPII contains four subunits (different in sequence from the COPI subunits), that includes a small GTPbinding protein, SAR1.…”

Expanding Proteostasis by Membrane Trafficking Networks

“…Moreover, the CTF system forms dynamic complexes that control the temporal and spatial features of endomembrane architecture and function through the information encoded by the primary polypeptide sequence, but presented in the context of the fold (the secondary, tertiary, and quaternary structural features) of each cargo (Nishimura et al 1999;Miller and Barlowe 2010;Kelly and Owen 2011). The dynamic properties of CTF biology are illustrated by (1) the collapse of the Golgi into the ER in response to brefeldin A-mediated inhibition of COPI coat assembly; (2) the role of diverse cargo in managing CTF-based compartment identity (Springer and Schekman 1998;Aridor et al 1999;Mettlen et al 2010); (3) the role of small GTPases in regulating the trajectories of CTF complexes (Hutagalung and Novick 2011;Mizuno-Yamasaki et al 2012); and (4) the sensitivity of compartment architecture to diverse physiologically and environmentally triggered signaling pathways.…”

“…But, unlike cytosolic chaperonins and proteasomes that have relatively stable Anfinsen cage structures (Zhang et al 2010), Anfinsen compartments are temporally and spatially dynamic in composition and organization in response to the CTF composition ) and cargo content of each cell type (Fig. 3A) (Springer and Schekman 1998;Aridor et al 1999;Mettlen et al 2010). This is evident in, for example, the sequential CTF-based TRaCKS transiently engaged by the cystic fibrosis transmembrane conductance regulator (CTFR) to provide a precise trajectory for its trafficking from the ER to the plasma membrane (Tang et al 2011a), a process that is disrupted in disease ).…”