Abstract
Single-stranded DNA binding protein (SSB) plays an important role in DNA metabolism, such as DNA replication, repair, and recombination. SSB of Helicobacter pylori (HpSSB) is encoded by the ssb gene and contains 179 residues. The crystal structure of truncated HpSSB protein (residue 1-134) complexed with dT(pT)34 was determined at 3.1 □ resolution by X-ray crystallographic method. HpSSB exists as a tetramer in both crystal and solution states. The N-terminal domain (residue 1-115) contains an OB-fold (oligonucleotides binding fold), which is similar with other species like E. coli, to function as an ssDNA binding domain. However, the ssDNA binding mode of tmHpSSB134 exhibits a considerable variability with comparison to that of E. coli. In the structure of tmHpSSB134-dT(pT)34 complex, the ssDNA wraps on the OB-fold with mainly electrostatic and stacking interactions. Several basic residues, Arg10, Arg35, and Lsy108, on the surface of tmHpSSB134 form a significant patch to accommodate the ssDNA binding. Furthermore, two aromatic residues, Phe50 and Trp84, interact with thymidine by stacking interaction. The structure of residues 116-134 was unable to be determined because of its flexibility. Many evidences reveal that the acidic C-terminal tail of SSB might participate in the protein-protein interaction. The C-terminal interactions may trigger the activities of the associated proteins in DNA metabolism.