In the E. coli cytosol, a fraction of the newly synthesised proteins requires the activity of molecular chaperones for folding to the native state. The major chaperones implicated in this folding process are the ribosome-associated Trigger Factor (TF), and the DnaK and GroEL chaperones with their respective co-chaperones. Trigger Factor is an ATP-independent chaperone and displays chaperone and peptidyl-prolyl-cis-trans-isomerase (PPIase) activities in vitro. It is composed of three domains, an N-terminal domain which mediates association with the large ribosomal subunit (ribosome-binding domain, RBD), a central PPIase domain with homology to FKBP proteins, and a C-terminal substrate-binding domain (SBD) which forms the central body of the protein and has two helical arms that create a cavity [1,2]. The association between its N-terminal domain with the ribosomal protein L23 located next to the peptide tunnel exit is essential for the interaction with nascent polypeptides and its in vivo function [1]. This entry represents the C-terminal region of TF which has a multi-helical structure consisting of an irregular array of long and short helices structurally similar to the peptide-binding domain of the bacterial porin chaperone SurA [3].

1: Trigger Factor and DnaK possess overlapping substrate pools and binding specificities. Deuerling E, Patzelt H, Vorderwulbecke S, Rauch T, Kramer G, Schaffitzel E, Mogk A, Schulze-Specking A, Langen H, Bukau B; Mol Microbiol 2003;47:1317-1328. PMID:12603737

2: The dynamic dimer structure of the chaperone Trigger Factor. Morgado L, Burmann BM, Sharpe T, Mazur A, Hiller S; Nat Commun. 2017;8:1992. PMID:29222465

3: Inter-domain dynamics in the chaperone SurA and multi-site binding to its outer membrane protein clients. Calabrese AN, Schiffrin B, Watson M, Karamanos TK, Walko M, Humes JR, Horne JE, White P, Wilson AJ, Kalli AC, Tuma R, Ashcroft AE, Brockwell DJ, Radford SE; Nat Commun. 2020;11:2155. PMID:32358557