1mul
Crystal structure of the E. coli HU alpha2 protein
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OverviewOverview
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.
About this StructureAbout this Structure
1MUL is a Single protein structure of sequence from Escherichia coli. Full crystallographic information is available from OCA.
ReferenceReference
Evidence of a thermal unfolding dimeric intermediate for the Escherichia coli histone-like HU proteins: thermodynamics and structure., Ramstein J, Hervouet N, Coste F, Zelwer C, Oberto J, Castaing B, J Mol Biol. 2003 Aug 1;331(1):101-21. PMID:12875839
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