Individual Subunits of Bacterial Luciferase are Molten Globules and Interact with Molecular Chaperones

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 90; no. 22; pp. 10826 - 10830
• Main Authors: Flynn, Gregory C., Con J. M. Beckers, Baase, Walter A., Dahlquist, Frederick W.
• Format: Journal Article
• Language: English
• Published: Washington, DC National Academy of Sciences of the United States of America 15-11-1993; National Acad Sciences; National Academy of Sciences
• Subjects: Adenosine Triphosphate - metabolism; Amides; Bacteria; Bacterial Proteins - metabolism; Biochemistry; Biological and medical sciences; Chaperonin 10; Chaperonin 60; Circular Dichroism; Dimers; Enzymes; Escherichia coli; Escherichia coli - metabolism; Fundamental and applied biological sciences. Psychology; Globules; Heat-Shock Proteins - metabolism; In Vitro Techniques; Inclusion bodies; Luciferases - chemistry; Macromolecular Substances; Magnetic Resonance Spectroscopy; Molecular and cellular biology; Molecular chaperones; Molecular genetics; Molecules; Protein Conformation; Protein refolding; Protein Structure, Secondary; Proteins; Protons; Recombinant Proteins; Solubility; Spectrophotometry, Ultraviolet; Translation. Translation factors. Protein processing; Vibrio - enzymology; Heterologous system; Molecular processing; Enzyme; Escherichia coli; Luciferase; Chaperone; Subunit; Precursor; Mechanism; Proteins; Vibrio harveyi; Molecular assembly; Bacteria; Vibrionaceae; Enterobacteriaceae
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.90.22.10826

We have studied the assembly of a large heterodimeric protein, bacterial luciferase, by mixing purified subunits expressed separately in bacteria. The individual subunits α and β contain much (66% and 50%, respectively) of the α-helix content of the native heterodimer as measured by circular dichroism, yet the α subunit lacks observable tertiary structure as measured by NMR. These results are consistent with the α subunit existing in a molten globule or collapsed form prior to assembly. The molecular chaperone GroEL binds reversibly to both subunits prior to assembly. Since these observations were obtained under physiological conditions, we propose that the molten globule exists as a stable form during folding or assembly in the cell. Either the molten globule form of the subunits is an authentic folding intermediate or it is in rapid equilibrium with one. GroEL may function by facilitating assembly through stabilization of these incompletely folded subunits.