Allosteric regulation of Arf GTPases and their GEFs at the membrane interface

Abstract

Arf GTPases assemble protein complexes on membranes to carry out major functions in cellular traffic. An essential step is their activation by guanine nucleotide exchange factors (GEFs), whose Sec7 domain stimulates GDP/GTP exchange. ArfGEFs form 2 major families: ArfGEFs with DCB, HUS and HDS domains (GBF1 and BIG1/BIG2 in humans), which act at the Golgi; and ArfGEFs with a Cterminal PH domain (cytohesin, EFA6 and BRAG), which function at the plasma membrane and endosomes. In addition, pathogenic bacteria encode an ArfGEF with a unique membrane-binding domain. Here we review the allosteric regulation of Arf GTPases and their GEFs at the membrane interface. Membranes contribute several regulatory layers: at the GTPase level, where activation by GTP is coupled to membrane recruitment by a built-in structural device; at the Sec7 domain, which manipulates this device to ensure that Arf-GTP is attached to membranes; and at the level of noncatalytic ArfGEF domains, which form direct or GTPase-mediated interactions with membranes that enable a spectacular diversity of regulatory regimes. Notably, we show here that membranes increase the efficiency of a large ArfGEF (human BIG1) by 32-fold by interacting directly with its Nterminal DCB and HUS domains. The diversity of allosteric regulatory regimes suggests that ArfGEFs can function in cascades and circuits to modulate the shape, amplitude and duration of Arf signals in cells. Because Arf-like GTPases feature autoinhibitory elements similar to those of Arf GTPases, we propose that their activation also requires allosteric interactions of these elements with membranes or other proteins.

Proteomic Screen for Cellular Targets of the Vaccinia Virus F10 Protein Kinase Reveals that Phosphorylation of mDia Regulates Stress Fiber Formation

“…GBF1 (Golgi-specific brefeldin A resistance factor 1) is a guanine nucleotide exchange factor (GEF) for Arf1 and perhaps Arf5. It's most highly validated role is in the Arf1-mediated assembly of the COPI coat for Golgito-ER retrograde transport (64). Interestingly, the formation of vaccinia virus mature virions (MV) is resistant to brefeldin A (65).…”

The Arf GEF GBF1 and Arf4 synergize with the sensory receptor cargo, rhodopsin, to regulate ciliary membrane trafficking

“…The cognate-activating Arf GEFs principally control the membrane association of Arfs (Bui et al, 2009;Casanova, 2007;Nawrotek et al, 2016;Stalder and Antonny, 2013), but their membrane recruitment also involves protein interactions that include SNAREs and the ciliary cargo (Honda et al, 2005;Mazelova et al, 2009). Initially, Arf1 weakly associates with membranes through the N-terminal myristoyl group, but GEF activation and GTP binding cause a conformational transition, termed the 'myristoyl switch', which tightly couples Arf1 activation with stable membrane association (Antonny et al, 1997;Franco et al, 1996;Goldberg, 1998;Pasqualato et al, 2002;Randazzo et al, 1995).…”

“…Golgi-localized large Arf GEFs are autoinhibited in solution. Their catalytic activity and membrane association are controlled by cooperative allosteric regulation via coincidence detection by dimerization and cyclophillin-binding (DCB) and homology downstream of Sec7 (HDS) domains, which integrate direct inputs from membranes and multiple activated Arfs and Rabs Bouvet et al, 2013;McDonold and Fromme, 2014;Monetta et al, 2007;Nawrotek et al, 2016;Stalder and Antonny, 2013). GBF1 and Arf4 function within the early Golgi, and at the TGN (Ben-Tekaya et al, 2010;Chun et al, 2008;Garcia-Mata et al, 2003;Kawamoto et al, 2002;Mazelova et al, 2009;Nakai et al, 2013;Szul et al, 2005Szul et al, , 2007Wang et al, 2012;Zhao et al, 2006).…”

Nonselective Chemical Inhibition of Sec7 Domain-Containing ARF GTPase Exchange Factors

“…Besides interfering with the function of the Sec7 domain, multiple other regulatory mechanisms of ARF-GEF activity and membrane recruitment have been described (Wright et al, 2014;Nawrotek et al, 2016) and might potentially be hampered by Secdin. Growing evidence hints at the regulatory roles of the other conserved protein domains in addition to Sec7.…”

“…The Arabidopsis thaliana genome encodes three members of the GBF/Gea subfamily (GNOM,, and GNL2) and five BIG/Sec7related proteins (BIG1 to BIG5). Besides the catalytic Sec7 domain, the large ARF-GEFs share several other conserved protein motifs that have regulatory functions as protein-protein interaction platforms and define their endomembrane localization (Mouratou et al, 2005;Bui et al, 2009;Wright et al, 2014;Nawrotek et al, 2016). Much experimental evidence indicates that members of the two protein subfamilies of Arabidopsis ARF-GEFs have overlapping functions and can complement each other.…”