Evidence of a thermal unfolding dimeric intermediate for the Escherichia coli histone-like HU proteins: thermodynamics and structure.


The Escherichia coli histone-like HU protein pool is composed of three dimeric forms: two homodimers, EcHUalpha(2) and EcHUbeta(2), and a heterodimer, EcHUalphabeta. The relative abundance of these dimeric forms varies during cell growth and in response to environmental changes, suggesting that each dimer plays different physiological roles. Here, differential scanning calorimetry and circular dichroism (CD) were used to study the thermal stability of the three E.coli HU dimers and show that each of them has its own thermodynamic signature. Unlike the other HU proteins studied so far, which melt through a single step (N(2)<-->2D), this present thermodynamic study shows that the three E.coli dimers melt according to a two-step mechanism (N(2)<-->I(2)<-->2D). The native dimer, N(2), melts partially into a dimeric intermediate, I(2), which in turn yields the unfolded monomers, D. In addition, the crystal structure of the EcHUalpha(2) dimer has been solved. Comparative thermodynamic and structural analysis between EcHUalpha(2) and the HU homodimer from Bacillus stearothermophilus suggests that the E.coli dimer is constituted by two subdomains of different energetic properties. The CD study indicates that the intermediate, I(2), corresponds to an HU dimer having partly lost its alpha-helices. The partially unfolded dimer I(2) is unable to complex with high-affinity, single-stranded break-containing DNA. These structural, thermodynamic and functional results suggest that the N(2)<-->I(2) equilibrium plays a central role in the physiology of E.coli HU. The I(2) molecular species seems to be the EcHUbeta(2) preferential conformation, possibly related to its role in the E.coli cold-shock adaptation. Besides, I(2) might be required in E.coli for the HU chain exchange, which allows the heterodimer formation from homodimers. Study holds ProTherm entries: 16413, 16414, 16415, 16416, 16417, 16418, 16419, 16420, 16421, 16422, 16423, 16424, 16425, 16426, 16427, 16428, 16429, 16430 Extra Details: Transition 1; dimer alpha2; 0.1mM dithiotreitol was added in the experiment. HU; histone-like; thermal stability; DSC

Submission Details

ID: sonwg4MJ

Submitter: Connie Wang

Submission Date: April 24, 2018, 8:47 p.m.

Version: 1

Publication Details
Ramstein J;Hervouet N;Coste F;Zelwer C;Oberto J;Castaing B,J. Mol. Biol. (2003) Evidence of a thermal unfolding dimeric intermediate for the Escherichia coli histone-like HU proteins: thermodynamics and structure. PMID:12875839
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 UniProtKB Entries

Percent Identity Matching Chains Protein Accession Entry Name
100.0 DNA-binding protein HU-alpha P0ACF2 DBHA_ECO57
100.0 DNA-binding protein HU-alpha P0ACF1 DBHA_ECOL6
100.0 DNA-binding protein HU-alpha P0ACF0 DBHA_ECOLI
100.0 DNA-binding protein HU-alpha E0J6W8 DBHA_ECOLW
100.0 DNA-binding protein HU-alpha P0ACF3 DBHA_SHIFL
98.9 DNA-binding protein HU-alpha P0A1R7 DBHA_SALTI
98.9 DNA-binding protein HU-alpha P0A1R6 DBHA_SALTY
94.4 DNA-binding protein HU-alpha P52680 DBHA_SERMA