Co-Translational Membrane Targeting and Holo-Translocon Docking of Ribosomes Translating the SRP Receptor

• Published in: Journal of molecular biology 2022-03, Vol.434 (5), p.167459-167459, Article 167459
• Main Authors: Mayer, Michal, Winer, Lulu, Karniel, Amihai, Pinner, Elhanan, Yardeni, Eliane H., Morgenstern, David, Bibi, Eitan
• Format: Article
• Language: English
• Subjects: Bacterial Proteins - biosynthesis; Bacterial Proteins - chemistry; Bacterial Proteins - genetics; Cell Membrane - metabolism; Escherichia coli - genetics; Escherichia coli - metabolism; Escherichia coli Proteins - biosynthesis; Escherichia coli Proteins - chemistry; Escherichia coli Proteins - genetics; FtsY; holo-translocon; membrane protein biogenesis; membrane ribosomes; Molecular Chaperones - metabolism; Protein Binding; Protein Biosynthesis; Receptors, Cytoplasmic and Nuclear - biosynthesis; Receptors, Cytoplasmic and Nuclear - chemistry; Receptors, Cytoplasmic and Nuclear - genetics; Ribosomes - metabolism; SecA; SecDFYajC; SecYEG; Signal Recognition Particle - biosynthesis; Signal Recognition Particle - chemistry; Signal Recognition Particle - genetics; SRP-receptor; YfgM
• ISSN: 0022-2836; 1089-8638
• DOI: 10.1016/j.jmb.2022.167459

[Display omitted] •Ribosome-FtsY translation intermediates directly target the membrane-embedded holo-translocon.•Prior to membrane docking, ribosome-FtsY translation intermediates are associated with cytosolic chaperons.•Docking of ribosomes translating FtsY involves a variety of contacts with holo-translocon components.•The co-translational contacts of the FtsY nascent chains with the SecYEG translocon differ from its post-translational contacts with this machinery. Many integral membrane proteins are produced by translocon-associated ribosomes. The assembly of ribosomes translating membrane proteins on the translocons is mediated by a conserved system, composed of the signal recognition particle and its receptor (FtsY in Escherichia coli). FtsY is a peripheral membrane protein, and its role late during membrane protein targeting involves interactions with the translocon. However, earlier stages in the pathway have remained obscure, namely, how FtsY targets the membrane in vivo and where it initially docks. Our previous studies have demonstrated co-translational membrane-targeting of FtsY translation intermediates and identified a nascent FtsY targeting-peptide. Here, in a set of in vivo experiments, we utilized tightly stalled FtsY translation intermediates, pull-down assays and site-directed cross-linking, which revealed FtsY-nascent chain-associated proteins in the cytosol and on the membrane. Our results demonstrate interactions between the FtsY-translating ribosomes and cytosolic chaperones, which are followed by directly docking on the translocon. In support of this conclusion, we show that translocon over-expression increases dramatically the amount of membrane associated FtsY-translating ribosomes. The co-translational contacts of the FtsY nascent chains with the translocon differ from its post-translational contacts, suggesting a major structural maturation process. The identified interactions led us to propose a model for how FtsY may target the membrane co-translationally. On top of our past observations, the current results may add another tier to the hypothesis that FtsY acts stoichiometrically in targeting ribosomes to the membrane in a constitutive manner.