Complex interactions between the chaperonin 60 molecular chaperone and dihydrofolate reductase

• Published in: Biochemistry (Easton) Vol. 30; no. 40; pp. 9716 - 9723
• Main Authors: Viitanen, Paul V, Donaldson, Gail K, Lorimer, George H, Lubben, Thomas H, Gatenby, Anthony A
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 08.10.1991
• Subjects: Adenosine Triphosphate - physiology; Animals; Bacterial Proteins - chemistry; Bacterial Proteins - isolation & purification; Bacterial Proteins - pharmacology; Biological and medical sciences; Chaperonin 60; Conformational dynamics in molecular biology; dihydrofolate reductase; Enzyme Activation - drug effects; Enzyme Stability - drug effects; Escherichia coli - chemistry; Folic Acid Antagonists; Fundamental and applied biological sciences. Psychology; Heat-Shock Proteins - chemistry; Heat-Shock Proteins - isolation & purification; Heat-Shock Proteins - pharmacology; Macromolecular Substances; Mice; Molecular biophysics; Protein Conformation - drug effects; Tetrahydrofolate Dehydrogenase - chemistry; Tetrahydrofolate Dehydrogenase - isolation & purification; Structure activity relation; Enzyme; Proteolysis; Conformational dynamics; Tetrahydrofolate dehydrogenase; Molecular interaction; ATP; Induced conformation
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi00104a021

The spontaneous refolding of chemically denatured dihydrofolate reductase (DHFR) is completely arrested by chaperonin 60 (GroEL). This inhibition presumably results from the formation of a stable complex between chaperonin 60 and one or more intermediates in the folding pathway. While sequestered on chaperonin 60, DHFR is considerably more sensitive to proteolysis, suggesting a nonnative structure. Bound DHFR can be released from chaperonin 60 with ATP, and although chaperonin 10 (GroES) is not obligatory, it does potentiate the maximum effect of ATP. Hydrolysis of ATP is also not required for DHFR release since certain nonhydrolyzable analogues are capable of partial discharge. "Native" DHFR can also form a stable complex with chaperonin 60. However, in this case, complex formation is not instantaneous and can be prevented by the presence of DHFR substrates. This suggests that native DHFR exists in equilibrium with at least one conformer which is recognizable by chaperonin 60. Binding studies with 35S-labeled DHFR support these conclusions and further demonstrate that DHFR competes for a common saturable site with another protein (ribulose-1,5-bisphosphate carboxylase) known to interact with chaperonin 60.