Motif-based endomembrane trafficking

Endomembrane trafficking, which allows proteins and lipids to flow between the different endomembrane compartments, largely occurs by vesicle-mediated transport. Transmembrane proteins intended for transport are concentrated into a vesicle or carrier by undulation of a donor membrane. This is followed by vesicle scission, uncoating, and finally, fusion at the target membrane. Three major trafficking pathways operate inside eukaryotic cells: anterograde, retrograde, and endocytic. Each pathway involves a unique set of machinery and coat proteins that pack the transmembrane proteins, along with their associated lipids, into specific carriers. Adaptor and coatomer complexes are major facilitators that function in anterograde transport and in endocytosis. These complexes recognize the transmembrane cargoes destined for transport and recruit the coat proteins that help form the carriers. These complexes use either linear motifs or posttranslational modifications to recognize the cargoes, which are then packaged and delivered along the trafficking pathways. In this review, we focus on the different trafficking complexes that share a common evolutionary branch in Arabidopsis (Arabidopsis thaliana), and we discuss up-to-date knowledge about the cargo recognition motifs they use.

Trafficking protein complexes recognize specific linear motifs or modifications on integral membrane proteins and this recognition guides their transport between the different cellular compartments.

ADVANCED

• Plant research is slowly gaining insight into the linear trafficking motifs used by the various AP complexes.Recent observations point out that steady-state accumulation of cargo proteins at the plasma membrane is not necessarily caused by to impaired internalization.
• TSET/TPC, the most recently identified member of the heterotetrameric adaptor complex-containing coat (HTAC-CC) family, and the identification of an endocytic-autophagosomal degradation pathway operating between the contact sites of the endoplasmic reticulum with the plasma membrane and the vacuole provide previously undiscovered additional layers of complexity to endomembrane trafficking in plants.