3D structure of Thermus aquaticus single-stranded DNA-binding protein gives insight into the functioning of SSB proteins.
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 chi subunit of DNA polymerase III is proposed. It explains at a molecular level the reason for the ssb113 phenotype observed in Escherichia coli.
Fedorov
Roman
R
Institute for Biophysical Chemistry, Hannover Medical Schoo,l Carl-Neuberg-Strasse 1, D-30625 Hannover, Germany.
Witte
Gregor
G
Urbanke
Claus
C
Manstein
Dietmar J
DJ
Curth
Ute
U
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D018360:Crystallography, X-Ray; D004258:DNA Polymerase III / Q000737:chemistry; D004277:DNA, Single-Stranded / Q000737:chemistry; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017384:Sequence Deletion; D013824:Thermus
D001426:Bacterial Proteins; D004277:DNA, Single-Stranded; D004268:DNA-Binding Proteins; D004258:DNA Polymerase III