A COPI coat subunit interacts directly with an early‐Golgi localized Arf exchange factor

Abstract

Arf (ADP-ribosylation factor) family small G proteins are crucial regulators of intracellular transport. The active GTP-bound form of Arf interacts with a set of proteins-effectors-which mediate the downstream signalling events of Arf activation. A well-studied class of Arf1 effectors comprises the coat complexes, such as the cis-Golgi-localized COPI (coat protein complex I) coat, and transGolgi network-endosomal clathrin coats. At least five different coats require Arf1-GTP to localize to organelle membranes. How a single Arf protein recruits different coat complexes to distinct membrane sites raises the question of how specificity is achieved. Here, we propose a molecular mechanism of this specificity for the COPI coat by showing a direct and specific interaction between a COPI subunit and a cis-Golgi localized subfamily of Arf guanine nucleotide exchange factors (GEFs) that takes place independently of Arf1 activation. In this way, a specific output on Arf1 activation can be programmed before the exchange reaction by the GEF itself.

Dopamine receptor D 3 regulates endocytic sorting by a Prazosin-sensitive interaction with the coatomer COPI

“…S4), the mechanisms of action of Prazosin and Brefeldin involve the same protein complex, the coatomer COPI. Brefeldin has been used successfully to study Golgi dynamics (10). COPI localizes not only to the Golgi but also to small vesicles and the cytoplasm.…”

The phosphatidylinositol 4-kinase PI4KIIIα is required for the recruitment of GBF1 to Golgi membranes

“…In support of this, cells depleted of PtdIns(4)P or PI4KIII had little or no Golgi-localized GGA3. Because GBF1 is also implicated in the recruitment of COPI to Golgi membranes (Alvarez et al, 2003;Deng et al, 2009), we predict that but have not tested whether the depletion of PtdIns(4)P would also affect the recruitment of the COPI complex. A previous study has shown that PtdIns(4)P produced by PI4KII, a Golgi-localized PI4K, is required for GGA recruitment (Wang et al, 2007).…”

“…GEFs are localized to and recruited to specific membranes, and it is this step that is believed to control the specificity of the activation of Arfs. The large ArfGEF GBF1 is an activator of Arf1, and is required for the recruitment of both the COPI complex (Alvarez et al, 2003;Deng et al, 2009) and the GGAs (Lefrancois and McCormick, 2007), whereas the GEF BIG2, which also activates Arf1, has been implicated in the recruitment 2277 PtdIns(4)P is required for GBF1 recruitment Fig. 6.…”

“…Arf1 is involved in the recruitment of COPI (Dascher and Balch, 1994), the Golgilocalized -ear-containing, Arf-binding proteins (GGAs) and adaptor protein (AP)-1 to Golgi membranes (Dell'Angelica et al, 2000a;Traub et al, 1993), and AP-3 to endosomal membranes (Ooi et al, 1998). The specificity of this recruitment depends on the GEFs; recent evidence has shown that BIG2 is involved in the recruitment of AP-1 (Shinotsuka et al, 2002), whereas GBF1 is required for the recruitment of COPI (Alvarez et al, 2003;Deng et al, 2009) and the GGAs to Golgi membranes (Lefrancois and McCormick, 2007). The interaction of GBF1 with membranes of the Golgi is required for the conversion of Arf1-GDP to Arf1-GTP (Niu et al, 2005).…”

The Golgi apparatus: insights from filamentous fungi

“…Yeast late Golgi Sec7, for example, has been shown to regulate and/or integrate feedbacks from multiple master Golgi regulators (Arl1, Arf1, Ypt1, Ypt31/32), resulting in coordination of Golgi functions, especially of Golgi entry and exit (McDonold and Fromme 2014). Yeast early Golgi Gea1p has been shown to interact with a subunit of CopI (Deng et al 2009), an Arf1 effector that has roles in intra-Golgi and Golgi-to-ER traffic. Apart from their largely unexplored roles, the specific membrane recruitment mechanism of Golgi Arf1 GEFs (they are peripheral membrane proteins) to specialized Golgi subcompartments is not understood (Wright et al 2014).…”