Small G Proteins: Arf Family GTPases in Vesicular Transport - Ras Superfamily Small G Proteins: Biology and Mechanisms 2 - page 190

Fig. 9.1 Individual steps in the life cycle of COPI vesicles. Arf is recruited to donor membranes
by interaction with dimeric cytoplasmic tails of membrane machinery proteins (e.g. p23 or p24).
Subsequently, Arf is anchored to the membrane by activation via the GEF GBF1. On membranes,
Arf1-GTP can form a homodimer. Efficient cargo uptake (but not uptake of machinery proteins)
requires GTP hydrolysis by an unknown mechanism. Membrane-bound Arf recruits en bloc the
coat complex coatomer. Dimeric p24 proteins bind to sites within the trunk and appendage
domains of

ʲ 0 -COPs. Binding

ʳ -COP. Cargo proteins bind to distinct binding sites in α -COP and

of dimeric p24 proteins to the trunk domain of ʳ -COP induces a conformational change of

coatomer, which is transmitted to -COP and triggers coat polymerisation. Vesicle scission

requires membrane curvature potentiating activity of the (oligomerised) small GTPase Arf1.
ArfGAP-stimulated GTP hydrolysis leads to release of the small GTPase and subsequent release
of the coat

α