Abstract

Single-stranded DNA-binding proteins (SSBs) are indispensable elements in the cells of all living organisms. SSB proteins interact with ssDNA insequence in an independent manner, preventing them from forming secondary structures and from degradation by nucleases. In this way, SSB-binding proteins participate in all processes involving ssDNA, such as replication, repair and recombination. Although there are differences in amino acid sequences, SSBs have a high-conservative domain, the oligonucleotide/oligosaccharide–binding fold, referred to as the OB-fold, which is responsible for binding with ssDNA. In the single-stranded DNA-binding proteins described so far, four OB-fold domains form an active protein. These proteins have also the ability to bind RNA and are present in all three branches of live organisms and in viruses. The cooperative binding of single-strand DNA and RNA which is a property of SSBs has led to their being used as tools in molecular biology methods and analytics. Thermostable proteins are particularly useful in this respect. To date, only a few thermostable SSB proteins with these valuable applications have been identified and, as yet, no studies have been undertaken into single-strand binding proteins from cold-adapted organisms and their applications. 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 molecular mass of their monomers and length of amino acid sequences. The high level of identity and homology in respect of EcoSSB relates to the OB-fold and some of the last amino acid residues. The fluorescence titrations indicated that the ssDNA-binding site size is about 32 nucleotides long and is salt independent. The DpsSSB, FpsSSB, ParSSB, PcrSSB, PinSSB, PprSSB andPtoSSBcause the destabilization of duplex DNA, as expected. The greatest decrease of duplex DNA melting temperature was observed in the presence of PtoSSB (17°C). The investigated SSBs possess relatively high thermostability for the proteins derived from cold-adapted bacteria.

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