Effect of Mg2+ on the DNA binding modes of the Streptococcus pneumoniae SsbA and SsbB proteins

Diane E. Grove, Floyd R. Bryant

Research output: Contribution to journalArticlepeer-review

Abstract

The effect of Mg2+ on the binding of the Streptococcus pneumoniae single-stranded DNA binding (SSB) proteins, SsbA and SsbB, to various dTn oligomers was examined by polyacrylamide gel electrophoresis. The results were then compared with those that were obtained with the well characterized SSB protein from Escherichia coli, SsbEc. In the absence of Mg2+, the results indicated that the SsbEc protein was able to bind to the dTn oligomers in the SSB35 mode, with only two of the four subunits of the tetramer interacting with the dTn oligomers. In the presence of Mg2+, however, the results indicated that the SsbEc protein was bound to the dTn oligomers in the SSB65 mode, with all four subunits of the tetramer interacting with the dTn oligomers. The SsbA protein behaved similarly to the SsbEc protein under all conditions, indicating that it undergoes Mg2+-dependent changes in its DNA binding modes that are analogous to those of the SsbEc protein. The SsbB protein, in contrast, appeared to bind to the dTn oligomers in an SSB65-like mode in either the presence or the absence of Mg 2+, suggesting that it may not exhibit the pronounced negative intrasubunit cooperativity in the absence of Mg2+ that is required for the formation of the SSB35 mode. Additional experiments with a chimeric SsbA/B protein indicated that the structural determinants that govern the transitions between the different DNA binding modes may be contained within the N-terminal domains of the SSB proteins.

Original languageEnglish (US)
Pages (from-to)2087-2094
Number of pages8
JournalJournal of Biological Chemistry
Volume281
Issue number4
DOIs
StatePublished - Jan 27 2006

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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