Multistate equilibrium unfolding of Escherichia coli dihydrofolate reductase: thermodynamic and spectroscopic description of the native, intermediate, and unfolded ensembles.


Abstract

The thermodynamic and spectroscopic properties of a cysteine-free variant of Escherichia coli dihydrofolate reductase (AS-DHFR) were investigated using the combined effects of urea and temperature as denaturing agents. Circular dichroism (CD), absorption, and fluorescence spectra were recorded during temperature-induced unfolding at different urea concentrations and during urea-induced unfolding at different temperatures. The first three vectors obtained by singular-value decomposition of each set of unfolding spectra were incorporated into a global analysis of a unique thermodynamic model. Although individual unfolding profiles can be described as a two-state process, a simultaneous fit of 99 vectors requires a three-state model as the minimal scheme to describe the unfolding reaction along both perturbation axes. The model, which involves native (N), intermediate (I), and unfolded (U) states, predicts a maximum apparent stability, DeltaG degrees (NU), of 6 kcal mol(-)(1) at 15 degrees C, an apparent m(NU) value of 2 kcal mol(-)(1) M(-)(1), and an apparent heat capacity change, DeltaC(p)()(-NU), of 2.5 kcal mol(-)(1) K(-)(1). The intermediate species has a maximum stability of approximately 2 kcal mol(-)(1) and a compactness closer to that of the native than to that of the unfolded state. The population of the intermediate is maximal ( approximately 70%) around 50 degrees C and falls below the limits of detection of > or =2 M urea or at temperatures of <35 or >65 degrees C. The fluorescence properties of the equilibrium intermediate resemble those of a transient intermediate detected during refolding from the urea-denatured state, suggesting that a tryptophan-containing hydrophobic cluster in the adenosine-binding domain plays a key role in both the equilibrium and kinetic reactions. The CD spectroscopic properties of the native state reveal the presence of two principal isoforms that differ in ligand binding affinities and in the packing of the adenosine-binding domain. The relative populations of these species change slightly with temperature and do not depend on the urea concentration, implying that the two native isoforms are well-structured and compact. Global analysis of data from multiple spectroscopic probes and several methods of unfolding is a powerful tool for revealing structural and thermodynamic properties of partially and fully folded forms of DHFR. Study holds ProTherm entries: 8559, 8560 Extra Details: additive : K2EDTA(0.2 mM),C85A/C152S cysteine-free double mutant of,dihydrofolate reductase. N-><-I

Submission Details

ID: kibdqBnn3

Submitter: Connie Wang

Submission Date: April 24, 2018, 8:36 p.m.

Version: 1

Publication Details
Ionescu RM;Smith VF;O'Neill JC;Matthews CR,Biochemistry (2000) Multistate equilibrium unfolding of Escherichia coli dihydrofolate reductase: thermodynamic and spectroscopic description of the native, intermediate, and unfolded ensembles. PMID:10924151
Additional Information

Structure view and single mutant data analysis

Study data

No weblogo for data of varying length.
Colors: D E R H K S T N Q A V I L M F Y W C G P
 

Data Distribution

Studies with similar sequences (approximate matches)

Correlation with other assays (exact sequence matches)


Relevant PDB Entries

Structure ID Release Date Resolution Structure Title
6CW7 2018-03-30T00:00:00+0000 1.03 E. coli DHFR product complex with (6S)-5,6,7,8-TETRAHYDROFOLATE
6CXK 2018-04-03T00:00:00+0000 1.11 E. coli DHFR substrate complex with Dihydrofolate
6CYV 2018-04-06T00:00:00+0000 1.3 E. coli DHFR ternary complex with NADP and dihydrofolate
1DDR 1995-06-29T00:00:00+0000 2.45 MOLECULE: DIHYDROFOLATE REDUCTASE (E.C.1.5.1.3) COMPLEXED WITH METHOTREXATE AND UREA
1DDS 1995-06-29T00:00:00+0000 2.2 MOLECULE: DIHYDROFOLATE REDUCTASE (E.C.1.5.1.3) COMPLEXED WITH METHOTREXATE
1DHI 1993-10-29T00:00:00+0000 1.9 LONG-RANGE STRUCTURAL EFFECTS IN A SECOND-SITE REVERTANT OF A MUTANT DIHYDROFOLATE REDUCTASE
1DHJ 1993-10-29T00:00:00+0000 1.8 LONG-RANGE STRUCTURAL EFFECTS IN A SECOND-SITE REVERTANT OF A MUTANT DIHYDROFOLATE REDUCTASE
1DRA 1991-11-06T00:00:00+0000 1.9 CRYSTAL STRUCTURE OF UNLIGANDED ESCHERICHIA COLI DIHYDROFOLATE REDUCTASE. LIGAND-INDUCED CONFORMATIONAL CHANGES AND COOPERATIVITY IN BINDING
1DRB 1991-11-06T00:00:00+0000 1.96 CRYSTAL STRUCTURE OF UNLIGANDED ESCHERICHIA COLI DIHYDROFOLATE REDUCTASE. LIGAND-INDUCED CONFORMATIONAL CHANGES AND COOPERATIVITY IN BINDING
1DRE 1996-11-28T00:00:00+0000 2.6 DIHYDROFOLATE REDUCTASE COMPLEXED WITH METHOTREXATE AND NICOTINAMIDE ADENINE DINUCLEOTIDE PHOSPHATE (OXIDIZED FORM)

Relevant UniProtKB Entries

Percent Identity Matching Chains Protein Accession Entry Name
91.8 Dihydrofolate reductase P31074 DYR_KLEAE
96.2 Dihydrofolate reductase P31073 DYR_CITFR
100.0 Dihydrofolate reductase P0ABQ6 DYR_SHIFL
100.0 Dihydrofolate reductase P0ABQ4 DYR_ECOLI
100.0 Dihydrofolate reductase P0ABQ5 DYR_ECOL6