Luciferase Assembly after Transport into Mammalian Microsomes Involves Molecular Chaperones and Peptidyl-Prolyl cis/trans-Isomerases

The assembly of a heterodimeric luciferase was studied after de novo synthesis of corresponding precursor proteins in reticulocyte lysate and concomitant transport into dog pancreas microsomes. This cytosolic luciferase from a prokaryotic organism ( Vibrio harveyi ) was specifically used as a model protein to investigate (i) whether the eukaryotic cytosol and the microsomal lumen have similar folding capabilities and (ii) whether the requirements of a polypeptide for certain molecular chaperones and folding catalysts are determined by the polypeptide or the intracellular compartment. The two luciferase subunits were fused to the preprolactin signal peptide. Data indicate that efficient assembly of luciferase occurs in the mammalian microsomes. Furthermore, it was observed that luciferase assembly can be separated in time from synthesis and membrane transport, depends on ATP hydrolysis, is partially sensitive to cyclosporin A and FK506, and in the absence of lumenal proteins is less efficient as compared with the presence of lumenal proteins. Thus, heterodimeric luciferase depends on functionally related molecular chaperones and folding catalysts during its assembly in either the eukaryotic cytosol or the microsomal lumen.