Thermal Stability and DNA Binding Activity of a Variant Form of the Sso7d Protein from the Archeon Sulfolobus solfataricus Truncated at Leucine 54

摘要

Sso7d is a 62-residue, basic protein from the hyperthermophilic archaeon Sulfolobus solfataricus. Around neutral pH, it exhibits a denaturation temperature close to 100 deg C and a non-sequence-specific DNA binding activity. Here, we report the characterization by circular dichroism and fluorescence measurements of a variant form of Sso7d truncated at leucine 54 (L54DELGA). It is shown that L54DELTA has a folded conformatoion at neutral pH and that its thermal unfolding is reversible process, represented well by the two-state N <=> D transition model, with a denaturation temperature of 53 deg C. Fluorescence titration experiments indicate that L54 DELTA binds tightly to calf thymus DNA, even though the binding parameters are smaller than those of the wild-type protein. Therefore, the truncation of eight residues at the C-terminus of Sso7d markedly affects the thermal stability of the protein, which nevertheless retains a folded structure and DNA binding activity.