RT Journal Article
SR Electronic
T1 Cotranslational folding of a pentarepeat β-helix protein
JF bioRxiv
FD Cold Spring Harbor Laboratory
SP 255810
DO 10.1101/255810
A1 Luigi Notari
A1 Markel Martínez-Carranza
A1 Pål Stenmark
A1 Gunnar Von Heijne
YR 2018
UL http://biorxiv.org/content/early/2018/01/29/255810.abstract
AB It is becoming increasingly clear that many proteins start to fold cotranslationally, even before the entire polypeptide chain has been synthesized on the ribosome. One class of proteins that a priori would seem particularly prone to cotranslational folding is repeat proteins, i.e., proteins that are built from a linear array of nearly identical folding units. However, while the folding of repeat proteins has been studied extensively in vitro with purified proteins, only a handful of studies have addressed the issue of cotranslational folding of repeat proteins. Here, we have determined the structure and studied the cotranslational folding a β-helix pentarepeat protein from Clostridium botulinum, using an assay in which the SecM translational arrest peptide serves as a force sensor to detect folding events. We find that the folding nucleus involves the first four of the eight β-helix coils in the protein, and that folding starts when this folding nucleus is ~35 residues away from the P-site, near the mouth of the exit tunnel. The early cotranslational formation of a folded nucleus from which the β-helix can grow may be important to avoid misfolding events in vivo.Significance statement It has long been thought that many proteins start to fold cotranslationally as they come off the ribosome, before the entire chain has been synthesized. However, the overwhelming majority of experimental studies of protein folding have been carried out in vitro, using purified proteins. Here, we use an assay that allows us to detect the force that a cotranslationally folding protein exerts on the nascent polypeptide chain to follow the folding of a β-helix repeat protein as it emerges from the ribosome exit tunnel. We find that only four of the eight β-coils of the protein need to be present for the protein to start folding, and that this folding intermediate is formed near the mouth of the exit tunnel.