Characterization of single-stranded DNA-binding proteins from the psychrophilic bacteria Desulfotalea psychrophila, Flavobacterium psychrophilum, Psychrobacter arcticus, Psychrobacter cryohalolentis, Psychromonas ingrahamii, Psychroflexus torquis, and Photobacterium profundum

Abstract

Background

Single-stranded DNA-binding proteins (SSBs) play essential roles in DNA replication, recombination and repair in Bacteria, Archaea and Eukarya. In recent years, there has been an increasing interest in SSBs, since they find numerous applications in diverse molecular biology and analytical methods.

Results

We report the characterization of single-stranded DNA-binding proteins from the psychrophilic bacteria Desulfotalea psychrophila ( DpsSSB), Flavobacterium psychrophilum ( FpsSSB), Psychrobacter arcticus ( ParSSB), Psychrobacter cryohalolentis ( PcrSSB), Psychromonas ingrahamii ( PinSSB), Photobacterium profundum ( PprSSB), and Psychroflexus torquis ( PtoSSB). The proteins show a high differential within the molecular mass of their monomers and the length of their amino acid sequences. The high level of identity and similarity in respect to the EcoSSB is related to the OB-fold and some of the last amino acid residues. They are functional as homotetramers, with each monomer encoding one single stranded DNA binding domain (OB-fold). The fluorescence titrations indicated that the length of the ssDNA-binding site size is approximately 30 ± 2 nucleotides for the PinSSB, 31 ± 2 nucleotides for the DpsSSB, and 32 ± 2 nucleotides for the ParSSB, PcrSSB, PprSSB and PtoSSB. They also demonstrated that it is salt independent. However, when the ionic strength was changed from low salt to high, binding-mode transition was observed for the FpsSSB, at 31 ± 2 nucleotides and 45 ± 2 nucleotides, respectively. As expected, the SSB proteins under study cause duplex DNA destabilization. The greatest decrease in duplex DNA melting temperature was observed in the presence of the PtoSSB 17°C. The SSBs in question possess relatively high thermostability for proteins derived from cold-adapted bacteria.

Conclusion

The results showed that SSB proteins from psychrophilic microorganisms are typical bacterial SSBs and possess relatively high thermostability, offering an attractive alternative to other thermostable SSBs in molecular biology applications.