title: Protein conducting nanopores.
abstract: About 50% of the cellular proteins have to be transported into or across cellular membranes. This transport is an essential step in the protein biosynthesis. In eukaryotic cells secretory proteins are transported into the endoplasmic reticulum before they are transported in vesicles to the plasma membrane. Almost all proteins of the endosymbiotic organelles chloroplasts and mitochondria are synthesized on cytosolic ribosomes and posttranslationally imported. Genetic, biochemical and biophysical approaches led to rather detailed knowledge on the composition of the translocon-complexes which catalyze the membrane transport of the preproteins. Comprehensive concepts on the targeting and membrane transport of polypeptides emerged, however little detail on the molecular nature and mechanisms of the protein translocation channels comprising nanopores has been achieved. In this paper we will highlight recent developments of the diverse protein translocation systems and focus particularly on the common biophysical properties and functions of the protein conducting nanopores. We also provide a first analysis of the interaction between the genuine protein conducting nanopore Tom40(SC) as well as a mutant Tom40(SC) (S(54 --> E) containing an additional negative charge at the channel vestibule and one of its native substrates, CoxIV, a mitochondrial targeting peptide. The polypeptide induced a voltage-dependent increase in the frequency of channel closure of Tom40(SC) corresponding to a voltage-dependent association rate, which was even more pronounced for the Tom40(SC) S54E mutant. The corresponding dwelltime reflecting association/transport of the peptide could be determined with t(off) approximately = 1.1 ms for the wildtype, whereas the mutant Tom40(SC) S54E displayed a biphasic dwelltime distribution (t(off)(-1) approximately = 0.4 ms; t(off)(-2) approximately = 4.6 ms).
authors.affiliation: Biophysics, Department of Biology/Chemistry, University of Osnabrueck, Germany.
authors.forename: Anke
authors.initials: A
authors.lastname: Harsman
authors.forename: Vivien
authors.initials: V
authors.lastname: Krüger
authors.forename: Philipp
authors.initials: P
authors.lastname: Bartsch
authors.forename: Alf
authors.initials: A
authors.lastname: Honigmann
authors.forename: Oliver
authors.initials: O
authors.lastname: Schmidt
authors.forename: Sanjana
authors.initials: S
authors.lastname: Rao
authors.forename: Christof
authors.initials: C
authors.lastname: Meisinger
authors.forename: Richard
authors.initials: R
authors.lastname: Wagner
mesh_terms: D003198:Computer Simulation; D026901:Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D024101:Mitochondrial Proteins / Q000737:chemistry* / Q000648:ultrastructure*; D008956:Models, Chemical; D010455:Peptides / Q000737:chemistry*; D016062:Porosity; D021381:Protein Transport
chemical_list: D026901:Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D024101:Mitochondrial Proteins; D010455:Peptides; C000707766:Tomm40 protein, rat