ER-to-Golgi Transport: A Sizeable Problem

TLDR: Current models describing the dynamics and mechanisms of ER-Golgi transport are discussed, challenging long-held models of vesicular transport of large matrix proteins and are implicating less well-defined carriers and direct interconnections between organelles.

About: This article is published in Trends in Cell Biology.The article was published on 2019-12-01 and is currently open access. It has received 45 citations till now. The article focuses on the topics: Golgi apparatus & COPII.

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Table 1

Table 2: Evidence for COPII-dependency and other factors of the early secretory pathway influencing unconventional cargo transport from the ER to the Golgi (expanded from [2]).

Frequently asked questions

Q1. What is the role of Hsp47 in the export of procollagen?

101 Hsp47 can also bind to other small extracellular matrix proteins including decorin, fibromodulin, 102 and lumican [35] suggesting that it might play a role in their export from the ER. 

Q2. What is the importance of understanding the morphology and spatial organization of the ER-280?

The importance of understanding the morphology and spatial organization of the ER-280 ERGIC-Golgi interface tests their abilities to image cells using light and electron microscopy 281 methods. 

Q3. How many ER-Golgi experiments resulted in large carriers?

Most of the 196 experiments resulting in large carriers were performed in cells overexpressing KLHL12 and or 197 procollagens in transformed cell lines [11, 12]. 

Q4. How many extracellular proteins are required for a functional ECM?

Small molecule inhibitors, genetic depletion and knockout 70 experiments in both cells and animal models, as well as significant clinical data, have shown a 71 requirement for COPII proteins in the assembly of a functional ECM (Table 2, updated from [3]) [4-72 7]. 

Q5. What are the key features of the ER-Golgi interface?

Recent advances in gene engineering and super-resolution 21 microscopy have underscored the spatio-temporal organization of the ER-Golgi interface. 

Q6. How does the ER transfer to the next compartment?

Due to the limited space in 256 between the transitional ER and ERGIC and or Golgi elements it has also been proposed that 257 procollagen might transfer to the next compartment via a direct tunnel-like pathway [5, 78] 258 (Figure 2iv). 

Q7. What is the role of TANGO1 in ER-to-Golgi?

130TANGO1 in ER-to-Golgi transport of collagens 131The transport and Golgi organisation protein (TANGO1, encoded by the MIA3 gene) plays a key 132 role in ER to Golgi trafficking of large proteins and has drawn increasing attention in recent years. 

Q8. How many small punctate structures were detected in the early live cell?

221 Early live cell imaging of procollagen-GFP showed small punctate structures tracking along long 222 range curvilinear tracks throughout the cell [2]. 

Q9. What is the role of TANGO1 in the formation of large vesicle?

TANGO-related proteins 135 have also been implicated directly in the formation of large COPII-carriers that enable procollagen 136 transport from the ER [50-54]. 

Q10. What is the role of TANGO1 in the formation of tubules?

loading of Sar1 with non-hydrolysable 126 analogues of GTP also leads to tubule formation of artificial liposomes [41, 45-47]. 

Q11. what is the type of collagen in hsp47-null cells?

Y. et al. (2006) Type The authorcollagen in Hsp47-null cells is aggregated in endoplasmic 420 reticulum and deficient in N-propeptide processing and fibrillogenesis.