Protein translocation at the ER membrane: A complex process becomes more so

Protein transport across or insertion into a membrane is facilitated by multicomponent protein complexes that reside in the bilayer. Current models propose that these complexes mediate translocation and integration by an obligate sequence of interactions between the substrate polypeptide and other components. Recent discoveries extend and complicate these models, but, more importantly, they remind us that our current level of understanding of the actual molecular mechanisms involved is crude and represents only the tip of the iceberg.