This flexibility is often associated with the reduced stability of the psychrophilic protein. In comparison to their mesophilic equivalents,

selleck compound these proteins also often feature a higher Gly content; a lower basic amino acid content, particularly Arg, with a decreased Arg/(Arg + Lys)ratio; a lower Pro content, resulting from Pro deletion or substitution by other small KU55933 residues such as Ala, for example; fewer hydrogen bonds and aromatic interactions; and residues which are more polar, and less hydrophobic, resulting in the destabilization of the hydrophobic core. All these characteristics work together to increase the number of degrees of conformational freedom by introducing flexible residues on the protein surface and destabilizing the protein core by weakening the intermolecular forces. In this context, the DpsSSB, FpsSSB,

ParSSB, PcrSSB, PinSSB, PprSSB, and PtoSSB proteins have some cold adaptation qualities. With the exception of the PcrSSB and PprSSB, the proteins under study have a charged residues content of Asp, Glu, Lys, His and Arg, with DpsSSB at 24.5%, FpsSSB at 29.3%, ParSSB at 20.1%, PcrSSB at 18.3%, PinSSB at 21.2%, PprSSB at 18.0%, and PtoSSB at 30.4%) which is higher than the SSB from E. coli, at 19.7% (Table  3). Furthermore, the FpsSSB and PtoSSB share a charged amino acid residues content which is close to that of the TteSSB3, at 30.7%. In the thermophilic proteins, these residues may be involved in the ionic networks stabilization of the interdomain surface. In the DpsSSB, FpsSSB, ParSSB, PcrSSB, PinSSB, PprSSB and PtoSSB, the content of Arg residues and the Arg/(Arg + Lys) ratio are 7.0% and 0.63, 2.9% and 0.22, 4.7% and 0.53, Regorafenib mouse 4.6% and 0.55, 4.5% and 0.43, 4.4% and 0.54, and 2.6%

Resminostat and 0.20, respectively. These factors are definitely lower in the psychrophilic SSBs than in their mesophilic E. coli equivalent, at 5.6% and 0.62, with the exception of DpsSSB, and the thermophilic SSBs TteSSB3, at 6.0% and 0.53, and TmaSSB, at 10.6% and 0.75). This feature has been considered as a hallmark of psychrozymes [29–35]. The ability to form multiple salt bridges with acidic Asp and/or Glu amino acid residues and hydrogen bonds with other amino acids is normal for arginine. The decrease of Arg content, even the conservative replacement of Arg with Lys, entails a reduction in the number of salt bridges. Table 3 Percentage amino acid content of the SSB proteins under comparison SSB Ala Ile Leu Val Met Gly Pro Lys Arg Asp Glu Gln Asn Ser Thr His Trp Phe Tyr Cys DpsSSB 7.0 6.3 4.9 3.5 2.8 11.3 4.2 4.2 7.0 4.9 7.7 4.9 6.3 9.2 7.0 0.7 2.8 1.4 2.8 0.7 FpsSSB 4.3 7.9 5.0 6.4 2.1 6.4 2.1 10.0 2.9 5.0 9.3 2.1 7.1 8.0 10.7 2.1 1.4 4.3 3.6 1.4 ParSSB 8.0 5.2 3.3 2.8 1.9 16.4 4.7 4.2 4.7 5.6 4.2 12.2 8.0 5.6 4.2 1.4 0.9 3.3 3.3 0 PcrSSB 6.8 4.6 2.7 2.7 1.8 16.9 4.6 3.7 4.6 5.0 4.1 12.8 10.0 7.3 4.1 0.9 0.9 3.2 3.2 0 PinSSB 7.7 1.8 3.6 4.5 3.6 6.8 9.9 5.9 4.5 4.5 5.4 17.6 6.3 3.6 6.3 0.9 1.8 2.3 2.7 0.5 PprSSB 7.7 3.3 3.8 6.