, 2007). It illustrates that Csps and CSD fold proteins have retained a high degree of functional similarity.

In addition we observed that CspD expression in Ant5-2 increased at 37 °C and upon UV exposure (Fig. 2b and c), and as described previously (Yamanaka et al., 2001; Kim & Wood, 2010), the cells also become elongated at 37 °C (data not shown), indicating that the CspD in Ant5-2 is a selleck screening library stress-inducible protein. Because CspD in Ant5-2 shares structural similarity with E. coli CspD, it might retain the same function as DNA replication inhibitor at 37 °C. It has also been reported that PprM, a homolog of Csp and a homodimer like E. coli CspD, is involved in the expression of many protein(s) that are important for the radioresistance of Deinococcus radiodurans (Ohba et

al., 2009). In this study, we have shown that the overall fold of the predicted CspD monomer from Ant5-2 did not closely resemble those of click here other bacterial cold-shock proteins. In both E. coli CspA and Bs-CspB, each chain is folded into an independent three-dimensional biological unit whereas the predicted Ant5-2 CspD dimer is composed of the N-terminal residues 1–36 from one chain and the C-terminal residues 37–67 from the other chain. The stable dimer prediction was performed with the help of the hex 5.1 docking software, which is considered to be a more reliable platform for ‘protein–protein’ compared with ‘protein–ligand’ docking. The predicted CspD dimer from Ant5-2 was formed by the exchange of two β-strands between protein monomers, but formed a symmetric unit of 2 five-stranded β-barrels unlike Nm-Csp that form two asymmetric five-stranded β-barrels. Despite differences, the predicted CspD dimer in Ant5-2 had significant structural similarities with the Nm-Csp and Bs-CspB dimers (Ren et al., 2008), sharing the same folds as Morin Hydrate that of monomeric Csps. This implies that it binds to ssDNA in a similar fashion. As evident

from the electrostatic properties, the only DNA-binding region in the predicted tertiary structure of CspD dimer of Ant5-2 is the side of the β-barrel, which corresponds to the DNA-binding site in OB-fold proteins such as E. coli CspA and B. subtilis CspB. Although its theoretical pI is 5.6, the attractive potential for nucleic acids is created by the solvent-exposed basic amino acids located on the nucleic acid-binding surface. The solvent-exposed aromatic residues on the surface of these molecules also bind and melt nucleic acid secondary structure to facilitate transcription and translation at low temperatures (Phadtare et al., 2004). The phylogenetic relationship of the CspD from Ant5-2 and Csps from three classes of phylum Proteobacteria, i.e. Betaproteobacteria, Gammaproteobacteria and Firmicutes, revealed that they distinctly form orthologous protein groups indicating a speciation event at each node except E. coli CspD.