The evolution of protein targeting and translocation systems

Cells have evolved increasingly complex membrane systems for compartmentalization and thereby for the regulation of multiple cellular pathways. The existence of such membranes required the evolution of molecular machines that allow and regulate the exchange of material between intracellular compartments or with the exterior. Here, we have summarized the current concepts for the origin and evolution of the targeting and translocation systems required for the specific insertion of transmembrane proteins into their target membranes and for the transport of protein cargos across membranes. The basic pathways developed in prokaryotes were modified and extended to suffice for the much more complex membrane systems found in eukaryotes, allowing not only the identification of basic mechanistic principles, but also phylogenetic studies to elucidate evolutionary relations.

Research highlights
► translocating machines of the plasma membrane are evolutionary ancient.
► Chaperone system involved in protein transport evolved independent of the membrane inserted machines.
► Omp85 is the ancient outer membrane protein assembly machine.
► recycling of prokaryotic systems led to sorting and transport machineries in eukaryotes.