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

• Published in: Nucleic acids research Vol. 34; no. 22; pp. 6708 - 6717
• Main Authors: Fedorov, Roman, Witte, Gregor, Urbanke, Claus, Manstein, Dietmar J, Curth, Ute
• Format: Journal Article
• Language: English
• Published: England Oxford University Press 01.12.2006; Oxford Publishing Limited (England)
• Subjects: Amino Acid Sequence; amino acids; Bacterial Proteins - chemistry; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Binding Sites; conserved sequences; crystal structure; Crystallography, X-Ray; DNA Polymerase III - chemistry; DNA, Single-Stranded - chemistry; DNA-binding proteins; DNA-Binding Proteins - chemistry; DNA-Binding Proteins - genetics; DNA-Binding Proteins - metabolism; DNA-directed DNA polymerase; Escherichia coli; isomerization; Models, Molecular; molecular models; Molecular Sequence Data; mutants; phenotype; proline; Protein Conformation; protein secondary structure; Sequence Deletion; Structural Biology; Thermus; Thermus aquaticus
• ISSN: 0305-1048; 1362-4962
• DOI: 10.1093/nar/gkl1002

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 χ subunit of DNA polymerase III is proposed. It explains at a molecular level the reason for the ssb113 phenotype observed in Escherichia coli.