Protein conducting nanopores

Abstract

About 50% of the cellular proteins have to be transported into or across cellularmembranes. This transport is an essential step in the protein biosynthesis. In eukaryoticcells secretory proteins are transported into the endoplasmic reticulum before they aretransported in vesicles to the plasma membrane. Almost all proteins of the endosymbioticorganelles chloroplasts and mitochondria are synthesized on cytosolic ribosomes andposttranslationally imported. Genetic, biochemical and biophysical approaches led torather detailed knowledge on the composition of the translocon-complexes which catalyzethe membrane transport of the preproteins. Comprehensive concepts on the targeting andmembrane transport of polypeptides emerged, however little detail on the molecular natureand mechanisms of the protein translocation channels comprising nanopores hasbeen achieved. In this paper we will highlight recent developments of the diverseprotein translocation systems and focus particularly on the common biophysicalproperties and functions of the protein conducting nanopores. We also provide afirst analysis of the interaction between the genuine protein conducting nanoporeTom40SC as well asa mutant Tom40SC () containing an additional negative charge at the channel vestibule and one of itsnative substrates, CoxIV, a mitochondrial targeting peptide. The polypeptideinduced a voltage-dependent increase in the frequency of channel closure ofTom40SC corresponding to a voltage-dependent association rate, which was even more pronounced for theTom40SC S54E mutant. The corresponding dwelltime reflecting association/transport ofthe peptide could be determined with ms for the wildtype, whereas the mutantTom40SC S54E displayed a biphasic dwelltime distribution ( ms; ms).