title: Solution structure, stability, and nucleic acid binding of the hyperthermophile protein Sso10b2.
abstract: 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 (15)N relaxation data demonstrated that the protein adopts a beta(1)alpha(1)beta(2)alpha(2)beta(3)beta(4) topology with an IF-3-like fold. The protein dimerizes in solution at 30 degrees C via a hydrophobic surface defined by the C-terminal alpha(2)beta(3)beta(4) 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 beta-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 Sso10b2 with nucleic acid showed that the protein binds single-stranded DNA (K(d) of 3 x 10(-)(7) M) with higher affinity than RNA (1.3 x 10(-)(6) M) or double-stranded DNA (1.5 x 10(-)(5) M) in 10 mM KH(2)PO(4) (pH 7.0, 20 degrees C). NMR chemical shift perturbation data indicated that single-stranded DNA and RNA binding occurred across the same dimer interface and encompassed a surface defined by the C-terminal ends of the beta(1), beta(2), and beta(3) strands of each monomer.
authors.affiliation: Laboratory for Structural Biology, Department of Chemistry, Graduate Program in Biotechnology and Bioengineering, University of Alabama in Huntsville, Huntsville, Alabama 35899, USA.
authors.forename: Kalpesh
authors.initials: K
authors.lastname: Biyani
authors.forename: Mebrahtu A
authors.initials: MA
authors.lastname: Kahsai
authors.forename: Andrew T
authors.initials: AT
authors.lastname: Clark
authors.forename: Tracy L
authors.initials: TL
authors.lastname: Armstrong
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Edmondson
authors.forename: John W
authors.initials: JW
authors.lastname: Shriver
mesh_terms: D000595:Amino Acid Sequence; D019843:Archaeal Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D018360:Crystallography, X-Ray; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D019281:Dimerization; D006863:Hydrogen-Ion Concentration; D057927:Hydrophobic and Hydrophilic Interactions; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D009696:Nucleic Acids / Q000378:metabolism*; D011487:Protein Conformation; D017510:Protein Folding; D016945:Sulfolobus acidocaldarius / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D019843:Archaeal Proteins; D004268:DNA-Binding Proteins; D009696:Nucleic Acids; C119661:Sac10b protein, Sulfolobus acidocaldarius