3D structure of Thermus aquaticus single-stranded DNA?binding protein gives insight into the functioning of SSB proteins - DNA

3D structure of Thermus aquaticus single-stranded DNA?binding protein gives insight into the functioning of SSB proteins
December 5, 2006
Roman Fedorov, Gregor Witte, Claus Urbanke, Dietmar J. Manstein and Ute Curth*
Institute for Biophysical Chemistry, Hannover Medical School Carl-Neuberg-Strasse 1, D-30625 Hannover, Germany
Nucleic Acids Research
ABSTRACT
In contrast to the majority of tetrameric SSB proteins, the recently discovered SSB proteins from the Thermus/Deinoccus group form dimers. We solved the crystal structures of the SSB protein from Thermus aquaticus (TaqSSB) and a deletion mutant of the protein and show the structure of their ssDNA binding domains to be similar to the structure of tetrameric SSBs. Two conformations accompanied by proline cis?trans isomerization are observed in the flexible C-terminal region. For the first time, we were able to trace 6 out of 10 amino acids at the C-terminus of an SSB protein. This highly conserved region is essential for interaction with other proteins and we show it to adopt an extended conformation devoid of secondary structure. A model for binding this region to the subunit of DNA polymerase III is proposed. It explains at a molecular level the reason for the ssb113 phenotype observed in Escherichia coli.
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