title: Promiscuous targeting of polytopic membrane proteins to SecYEG or YidC by the Escherichia coli signal recognition particle.
abstract: Protein insertion into the bacterial inner membrane is facilitated by SecYEG or YidC. Although SecYEG most likely constitutes the major integration site, small membrane proteins have been shown to integrate via YidC. We show that YidC can also integrate multispanning membrane proteins such as mannitol permease or TatC, which had been considered to be exclusively integrated by SecYEG. Only SecA-dependent multispanning membrane proteins strictly require SecYEG for integration, which suggests that SecA can only interact with the SecYEG translocon, but not with the YidC insertase. Targeting of multispanning membrane proteins to YidC is mediated by signal recognition particle (SRP), and we show by site-directed cross-linking that the C-terminus of YidC is in contact with SRP, the SRP receptor, and ribosomal proteins. These findings indicate that SRP recognizes membrane proteins independent of the downstream integration site and that many membrane proteins can probably use either SecYEG or YidC for integration. Because protein synthesis is much slower than protein transport, the use of YidC as an additional integration site for multispanning membrane proteins may prevent a situation in which the majority of SecYEG complexes are occupied by translating ribosomes during cotranslational insertion, impeding the translocation of secretory proteins.
authors.affiliation: Institut für Biochemie und Molekularbiologie, Zentrum für Biochemie und Molekulare Zellforschung, Albert-Ludwigs-Universität Freiburg, 79104 Freiburg, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Welte
authors.forename: Renuka
authors.initials: R
authors.lastname: Kudva
authors.forename: Patrick
authors.initials: P
authors.lastname: Kuhn
authors.forename: Lukas
authors.initials: L
authors.lastname: Sturm
authors.forename: David
authors.initials: D
authors.lastname: Braig
authors.forename: Matthias
authors.initials: M
authors.lastname: Müller
authors.forename: Bettina
authors.initials: B
authors.lastname: Warscheid
authors.forename: Friedel
authors.initials: F
authors.lastname: Drepper
authors.forename: Hans-Georg
authors.initials: HG
authors.lastname: Koch
mesh_terms: D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D021381:Protein Transport; D012270:Ribosomes / Q000378:metabolism; D000069816:SEC Translocation Channels; D015398:Signal Transduction
chemical_list: D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D000069816:SEC Translocation Channels; C412443:YIDC protein, E coli