Abstract
ADP-ribosylation factor (Arf) and related small GTPases play crucial roles in membrane traffic within the exo- and endocytic pathways. Arf proteins in their GTP-bound state are associated with curved membrane buds and tubules, frequently together with effector coat proteins to which they bind. Here we report that Arf1 is found on membrane tubules originating from the Golgi complex where it colocalizes with COPI and GGA1 vesicle coat proteins. Arf1 also induces tubulation of liposomes in vitro. Mutations within the amino-terminal amphipathic helix (NTH) of Arf1 affect the number of Arf1-positive tubules in vivo and its property to tubulate liposomes. Moreover, hydrophilic substitutions within the hydrophobic part of its NTH impair Arf1-catalyzed budding of COPI vesicles in vitro. Our data indicate that GTP-controlled local induction of high curvature membranes is an important property of Arf1 that might be shared by a subgroup of Arf/Arl family GTPases.
Highlights
Membrane traffic in eukaryotic cells involves the formation of curved membrane buds and tubules that carry cargo from a donor to an acceptor compartment [1,2,3]
Arf1-eGFP (F5W) and Arf1-eGFP (F5W/Q71L) (Fig. 1, B and C; supplemental Fig. 1B) decorated numerous membrane tubules originating from Golgi donor compartments at a frequency about 3 times higher than that seen in cells expressing Arf1-eGFP (WT) (Fig. 1C)
Our data indicate that Arf1-GTP induces positive curvature on membranes, and this property appears to be related to its role in COPI vesicle budding
Summary
Membrane traffic in eukaryotic cells involves the formation of curved membrane buds and tubules that carry cargo from a donor to an acceptor compartment [1,2,3]. Based on these data and on the observation that the NTHs of other Arf/ Arl family members associate with tubular membranes in living cells we suggest that GTP-controlled local induction of high curvature membranes is an important property of Arf1 and related small GTPases.
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