Solution structure, stability, and nucleic Acid binding of the hyperthermophile protein sso10b2.

The Sso10b (or Alba) family of proteins is a conserved group of archaeal and eukaryotic proteins which are thought to play a role in both chromatin organization and RNA metabolism. We describe here the solution structure and properties of Sso10b2 from Sulfolobus solfataricus. NMR data including residual dipolar couplings and 15N relaxation data demonstrated that the protein adopts a β1α1β2α2β3β4 topology with an IF-3-like fold. The protein dimerizes in solution at 30 °C via a hydrophobic surface defined by the C-terminal α2β3β4 elements with a structure similar to one of the putative dimers indicated by previous crystal structures. DSC and circular dichroism data demonstrated an unusual two-state structural transition near the growth temperature which led to an increase in β-sheet content without dissociation of the dimer. The cooperativity of the transition exceeded that of a dimer at pH 7, demonstrating the presence of higher order oligomers near the growth temperature at pH 7. Reverse titrations of Sso...