Enzyme assembly after de novo synthesis in rabbit reticulocyte lysate involves molecular chaperones and immunophilins

The folding kinetics of two luciferases were studied after synthesis in reticulocyte lysates to investigate whether molecular chaperones and/or folding catalysts are involved in the folding reactions. Two bacterial luciferases were used as model proteins: heterodimeric Vibrio harveyi luciferase (LuxAB), and a monomeric luciferase fusion protein (Fab2). Data indicate that folding of these enzymes to the native state occurs in the translation system, and that the extent of folding can be quantified. It was found that (i) folding of LuxAB and Fab2 can clearly be separated in time from synthesis, (ii) folding of Fab2 and LuxAB is slow because it involves either transient (Fab2) or permanent (LuxAB) interaction of polypeptides, (iii) preservation of the assembly competent state of LuxA and/or LuxB and folding of Fab2 depend on ATP-hydrolysis, (iv) folding of Fab2 and LuxAB is partially sensitive to cyclosporin A (CsA) and FK506, i.e. inhibitors of two distinct peptidylprolyl cis/trans-isomerases. Thus, bacterial luciferases provide a unique system for direct measurement of the effects of ATP-dependent molecular chaperones on protein folding and enzyme assembly in reticulocyte lysates. Furthermore, these two luciferases provide the first direct evidence documenting the involvement of peptidylprolyl cis/trans-isomerases in protein biogenesis in a eukaryotic cytosol.