E. coli HU dimers dynamics studied by NMR

HU is a 2x90 residues, dimeric bacterial histone-like protein involved in chromosome compaction and other DNA-related processes. E. coli HU proteins are composed of three forms: two homodimers α2 and β2 (α and β sharing 70% of sequence identity) and one heterodimer (αβ). Dimeric forms relative abundance varies during cell growth and in response to environmental changes, suggesting that each dimer plays different physiological roles.

Unlike other HU proteins which melt through a single step (N2<=>2D), E. coli dimers melt according to a two-step mechanism (N2<=>I2<=>2D). The native dimer, N2, melts partially into a dimeric intermediate, I2, which in turn yields the unfolded monomers, D. Circular Dichroism studies indicate that the intermediate, I2, corresponds to an HU dimer having partly lost its a-helices.

Here we compared dynamic properties and structural features of E. Coli HU dimers at different temperatures in order to determine the secondary strutural elements still present in the I2 intermediate.

Isotopically labelled proteins (15N, 13C) have been used to perform backbone assignment for all dimeric forms using sequential triple-resonance experiments. 15N-HSQC at different temperatures (288-323K) were recorded .Intensity variations and chemical shift perturbations allow the identification of the secondary element lost in the intermediate I2 confirming the high dynamics of arms responsible for protein-DNA interactions and the thermal stability of HTH motif in all dimeric forms.