Transmembrane but not soluble helices fold inside the ribosome tunnel. Issue 1 (December 2018)

• Record Type: Journal Article
• Authors: Bañó-Polo, Manuel; Baeza-Delgado, Carlos; Tamborero, Silvia; Hazel, Anthony; Grau, Brayan; Nilsson, IngMarie; Whitley, Paul; Gumbart, James; Heijne, Gunnar; Mingarro, Ismael
• Is Part Of: Nature communications. Volume 9:Issue 1(2018)
• Page Start: 1
• Page End: 9
• Publication Date: 2018-12
• Subjects: Biology -- Periodicals; Physical sciences -- Periodicals; 505
• DOI: 10.1038/s41467-018-07554-7
• Languages: English
• ISSNs: 2041-1723

Abstract

Abstract Integral membrane proteins are assembled into the ER membrane via a continuous ribosome-translocon channel. The hydrophobicity and thickness of the core of the membrane bilayer leads to the expectation that transmembrane (TM) segments minimize the cost of harbouring polar polypeptide backbones by adopting a regular pattern of hydrogen bonds to form α-helices before integration. Co-translational folding of nascent chains into an α-helical conformation in the ribosomal tunnel has been demonstrated previously, but the features governing this folding are not well understood. In particular, little is known about what features influence the propensity to acquire α-helical structure in the ribosome. Using in vitro translation of truncated nascent chains trapped within the ribosome tunnel and molecular dynamics simulations, we show that folding in the ribosome is attained for TM helices but not for soluble helices, presumably facilitating SRP (signal recognition particle) recognition and/or a favourable conformation for membrane integration upon translocon entry. Integral membrane proteins are assembled into the ER membrane via the ribosome-translocon channel. Here authors use in vitro translation assays and MD simulations to show that folding in the ribosome is favorable for TM helices, but unfavorable for soluble helices.