title: Individual subunits of bacterial luciferase are molten globules and interact with molecular chaperones.
abstract: We have studied the assembly of a large heterodimeric protein, bacterial luciferase, by mixing purified subunits expressed separately in bacteria. The individual subunits alpha and beta contain much (66% and 50%, respectively) of the alpha-helix content of the native heterodimer as measured by circular dichroism, yet the alpha subunit lacks observable tertiary structure as measured by NMR. These results are consistent with the alpha 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.
authors.affiliation: Institute of Molecular Biology, University of Oregon, Eugene 97403.
authors.forename: G C
authors.initials: GC
authors.lastname: Flynn
authors.forename: C J
authors.initials: CJ
authors.lastname: Beckers
authors.forename: W A
authors.initials: WA
authors.lastname: Baase
authors.forename: F W
authors.initials: FW
authors.lastname: Dahlquist
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D001426:Bacterial Proteins / Q000378:metabolism*; D018835:Chaperonin 10; D018834:Chaperonin 60; D002942:Circular Dichroism; D004926:Escherichia coli / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000378:metabolism*; D066298:In Vitro Techniques; D008156:Luciferases / Q000737:chemistry*; D046911:Macromolecular Substances; D009682:Magnetic Resonance Spectroscopy; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins; D012995:Solubility; D013056:Spectrophotometry, Ultraviolet; D014733:Vibrio / Q000201:enzymology
chemical_list: D001426:Bacterial Proteins; D018835:Chaperonin 10; D018834:Chaperonin 60; D006360:Heat-Shock Proteins; D046911:Macromolecular Substances; D011994:Recombinant Proteins; D000255:Adenosine Triphosphate; D008156:Luciferases