R67 dihydrofolate reductase (DHFR) is an R-plasmid encoded enzyme that confers resistance to the antibacterial drug trimethoprim. This enzyme is not homologous in sequence or structure to chromosomal DHFRs. Equilibrium folding of tetrameric R67 DHFR was studied and found to be fully reversible. Formation of an inactive intermediate was assayed by loss of enzyme activity. Denaturation of the intermediate was monitored by concurrent changes in fluorescence and circular dichroism signals. Both transitions are protein concentration dependent. A simple model fitting these data is tetramer<==>2 dimers<==>4 unfolded monomers. No evidence for folded monomer was found. Global fitting of all the folding data yielded a delta GH2O of -9.63 kcal/mol for the initial transition and a delta GH2O of -12.35 kcal/mol for the second transition. In addition, thermal unfolding of tetrameric R67 DHFR was found to be reversible A folding intermediate also occurred during thermal unfolding as evidenced by the asymmetric endotherms and a delta Hcalorimetric/delta H(van't Hoff) ratio of 2.1. Study holds ProTherm entries: 4429, 4430, 4431 Extra Details: tetrameric R67 DHFR; enzyme activity; folding intermediate;,asymmetric endotherms
Submitter: Connie Wang
Submission Date: April 24, 2018, 8:25 p.m.
|Number of data points||7|
|Proteins||Dihydrofolate reductase type 2 ; Dihydrofolate reductase type 2|
|Assays/Quantities/Protocols||Experimental Assay: activity ; Experimental Assay: dHcal ; Experimental Assay: Tm ; Experimental Assay: activity temp:30.0 C ; Experimental Assay: dG_H2O|
|Libraries||Mutations for sequence VFPSNATFGMGDRVRKKSGAAWQGQIVGWYCTNLTPEGYAVESEAHPGSVQIYPVAALERIN|