Cargo selection in vesicular transport: the making and breaking of a coat

Intracellular traffic is mediated by vesicular/tubular carriers. The carriers are formed by the activity of cytosolic coat proteins that are recruited to their target membranes and deform these membranes into buds and vesicles. Specific interactions between recruited coat subunits and short peptide sequences (transport motifs) on cargo proteins direct the incorporation of cargo into budded vesicles. Here, we focus on cargo selection reactions mediated by COPII and AP-2/clathrin vesicle coat complexes to explore common mechanisms by which coat assembly support localized and selective cargo sorting. Recent findings suggest that multiple, low-affinity interactions are employed in a cooperative manner to support coat assembly and enable cargo recognition. Thus low-binding affinities between coat subunits and transport motifs are transiently transformed into high-avidity, multivalent and selective interactions at vesicle bud sites. The temporal and regulated nature of the interactions provide the key to cargo selection.