C-terminal 13-residue Truncation Induces Compact Trigger Factor Conformation and Severely Impairs its Dimerization Ability

Trigger factor (TF) is the first chaperone to interact with nascent chains and facilitate their folding within bacteria. TF possesses a three-state equilibrium in vivo: monomeric TF bound to ribosome, free monomeric, and dimeric TF in cytoplasm. TF consists of an N-terminal ribosome binding domain, a middle peptidyl-prolyl cis/ trans isomerase (PPIase) domain and a C-terminal domain involved in substrate binding and dimerization. Investigation of the effect of C-terminal 13 region on TF structure and function will help to further the understanding of its mechanism as a chaperone in vitro and in vivo. Here we present TF419, a TF mutant from which the C-terminal 13 residues were deleted to investigate the role of these residues in the structure stability and function of intact molecules. Small angle X-ray scattering (SAXS), fluorescence measurements and limited proteolysis results suggested that TF transitioned to a compact conformation when the C-terminal 13 residues were truncated. Further biochemical results reveal that TF dimerization was decreased as a result of the truncation. These results suggested that the C-terminal 13 residues play an important role in structural stability and chaperone function of TF.