title: Co- and post-translational translocation through the protein-conducting channel: analogous mechanisms at work?
abstract: Many proteins are translocated across, or integrated into, membranes. Both functions are fulfilled by the 'translocon/translocase', which contains a membrane-embedded protein-conducting channel (PCC) and associated soluble factors that drive translocation and insertion reactions using nucleotide triphosphates as fuel. This perspective focuses on reinterpreting existing experimental data in light of a recently proposed PCC model comprising a front-to-front dimer of SecY or Sec61 heterotrimeric complexes. In this new framework, we propose (i) a revised model for SRP-SR-mediated docking of the ribosome-nascent polypeptide to the PCC; (ii) that the dynamic interplay between protein substrate, soluble factors and PCC controls the opening and closing of a transmembrane channel across, and/or a lateral gate into, the membrane; and (iii) that co- and post-translational translocation, involving the ribosome and SecA, respectively, not only converge at the PCC but also use analogous mechanisms for coordinating protein translocation.
authors.affiliation: Howard Hughes Medical Institute.
authors.forename: Kakoli
authors.initials: K
authors.lastname: Mitra
authors.forename: Joachim
authors.initials: J
authors.lastname: Frank
authors.forename: Arnold
authors.initials: A
authors.lastname: Driessen
mesh_terms: D001105:Archaea / Q000378:metabolism; D001419:Bacteria / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D018360:Crystallography, X-Ray; D005057:Eukaryotic Cells / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D014176:Protein Biosynthesis; D011487:Protein Conformation; D021381:Protein Transport; D011506:Proteins / Q000378:metabolism*; D012270:Ribosomes / Q000378:metabolism; D000069816:SEC Translocation Channels; D018271:Signal Recognition Particle / Q000378:metabolism
chemical_list: D008565:Membrane Proteins; D011506:Proteins; D000069816:SEC Translocation Channels; D018271:Signal Recognition Particle