title: Dynamic interaction of the sec translocon with the chaperone PpiD.
abstract: The Sec translocon constitutes a ubiquitous protein transport channel that consists in bacteria of the three core components: SecY, SecE, and SecG. Additional proteins interact with SecYEG during different stages of protein transport. During targeting, SecYEG interacts with SecA, the SRP receptor, or the ribosome. Protein transport into or across the membrane is then facilitated by the interaction of SecYEG with YidC and the SecDFYajC complex. During protein transport, SecYEG is likely to interact also with the protein quality control machinery, but details about this interaction are missing. By in vivo and in vitro site-directed cross-linking, we show here that the periplasmic chaperone PpiD is located in front of the lateral gate of SecY, through which transmembrane domains exit the SecY channel. The strongest contacts were found to helix 2b of SecY. Blue native PAGE analyses verify the presence of a SecYEG-PpiD complex in native Escherichia coli membranes. The PpiD-SecY interaction was not influenced by the addition of SecA and only weakly influenced by binding of nontranslating ribosomes to SecYEG. In contrast, PpiD lost contact to the lateral gate of SecY during membrane protein insertion. These data identify PpiD as an additional and transient subunit of the bacterial SecYEG translocon. The data furthermore demonstrate the highly modular and versatile composition of the Sec translocon, which is probably essential for its ability to transport a wide range of substrates across membranes in bacteria and eukaryotes.
authors.affiliation: From the Institut für Biochemie und Molekularbiologie, ZBMZ, Faculty of Medicine, the Faculty of Biology, and.
authors.forename: Ilie
authors.initials: I
authors.lastname: Sachelaru
authors.affiliation: From the Institut für Biochemie und Molekularbiologie, ZBMZ, Faculty of Medicine, the Faculty of Biology, and.
authors.forename: Narcis-Adrian
authors.initials: NA
authors.lastname: Petriman
authors.affiliation: From the Institut für Biochemie und Molekularbiologie, ZBMZ, Faculty of Medicine, the Faculty of Biology, and the Spemann-Graduate School of Biology and Medicine, Albert-Ludwigs-Universität Freiburg, 79104 Freiburg, Germany.
authors.forename: Renuka
authors.initials: R
authors.lastname: Kudva
authors.affiliation: From the Institut für Biochemie und Molekularbiologie, ZBMZ, Faculty of Medicine, the Spemann-Graduate School of Biology and Medicine, Albert-Ludwigs-Universität Freiburg, 79104 Freiburg, Germany Hans-Georg.Koch@biochemie.uni-freiburg.de.
authors.forename: Hans-Georg
authors.initials: HG
authors.lastname: Koch
mesh_terms: D000251:Adenosine Triphosphatases / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D020285:Cryoelectron Microscopy; D004591:Electrophoresis, Polyacrylamide Gel; D029968:Escherichia coli Proteins / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D008958:Models, Molecular; D019696:Peptidylprolyl Isomerase / Q000378:metabolism*; D011485:Protein Binding; D021381:Protein Transport; D000069816:SEC Translocation Channels; D000081416:SecA Proteins
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D000069816:SEC Translocation Channels; D000251:Adenosine Triphosphatases; C530413:PpiD protein, E coli; D019696:Peptidylprolyl Isomerase; D000081416:SecA Proteins
keywords: Chaperone; Escherichia coli (E. coli); Periplasm; Protein Cross-linking; Protein Quality Control; Protein Sorting; Protein Translocation