Trigger Factor from the Psychrophilic Bacterium Psychrobacter frigidicola Is a Monomeric Chaperone

ABSTRACT In eubacteria, trigger factor (TF) is the first chaperone to interact with newly synthesized polypeptides and assist their folding as they emerge from the ribosome. We report the first characterization of a TF from a psychrophilic organism. TF from Psychrobacter frigidicola (TF Pf ) was cloned, produced in Escherichia coli , and purified. Strikingly, cross-linking and fluorescence anisotropy analyses revealed it to exist in solution as a monomer, unlike the well-characterized, dimeric E. coli TF (TF Ec ). Moreover, TF Pf did not exhibit the downturn in reactivation of unfolded GAPDH (glyceraldehyde-3-phosphate dehydrogenase) that is observed with its E. coli counterpart, even at high TF/GAPDH molar ratios and revealed dramatically reduced retardation of membrane translocation by a model recombinant protein compared to the E. coli chaperone. TF Pf was also significantly more effective than TF Ec at increasing the yield of soluble and functional recombinant protein in a cell-free protein synthesis system, indicating that it is not dependent on downstream systems for its chaperoning activity. We propose that TF Pf differs from TF Ec in its quaternary structure and chaperone activity, and we discuss the potential significance of these differences in its native environment.