9 requires two different orientations to form the oligomer. This ability of the C-terminus to adopt two conformations resides in the amino acid segment between the strands β 9 and β 10, Selleck APO866 which permits a hinge movement. Analysis of the C-terminus contacts in the MjHSP16.5 structure showed
that the segment between the strands β 9 and β 10 adopts a conformation stabilized by hydrogen bonds between the OεGlu137 and NεGln52 atoms, and the carbonyl oxygen of the Glu137 and NζLys142 atoms. Surprisingly, these contacts are not found in the wHSP16.9 structure, due to the presence of a second Pro residue at position 142 that enables the segment to fold into a stable motif, generating a 6-residue segment (KAEVKK) with high flexibility, which allows the hinge movement. In both Afe_1437 and Afe_1009 protein sequences, this segment does not contain a DAPT nmr proline residue at the same relative position, and the residues populating this segment have all the requirements to form a stable motif in the same way as the MjHSP16.5 structure. Thus, based on our structural findings, we suggest that both Afe_1437 and Afe_1009 proteins behave like the prokaryotic sHSP from M. jannaschii, adopting a 24-molecule hollow spherical shell. However, additional experimental data obtained using techniques that can provide insights into hydrodynamic behavior, such as dynamic light scattering,
ultra-centrifugation, size-exclusion chromatography and small angle X-ray scattering, are required to confirm our in silico predictions. Conclusions In this study, we have demonstrated that the expression level of the A. ferrooxidans Afe_1437 gene is considerable higher than that of the Afe_2172 gene, and that the three sHSP genes harbor possible σ32-dependent promoters. The three sHSPs from A. ferrooxidans are not recent paralogs, while the genes Afe_1437 and Afe_1009 can be PRIMA-1MET cost inherited horizontally by A. ferrooxidans. This suggests that the sHSPs encoded by Thalidomide Afe_1437 and Afe_1009 are more likely to act as molecular chaperones in the A. ferrooxidans
heat shock response. These findings were corroborated by molecular modeling showing that both Afe_1437 and Afe_1009 proteins behave like the prokaryotic sHSP from M. jannaschii, a well characterized sHSP with chaperone activity. Acknowledgements This work was supported by grant 02/07642-3 from Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP). DAR had a fellowship from Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES). LMMO received a research fellowship from Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq). References 1. Kelly DP, Wood AP: Reclassification of some species of Thiobacillus to the newly designated genera Acidithiobacillus gen. nov., Halothiobacillus gen. nov. and Thermithiobacillus gen. nov. Int J Syst Evol Microbiol 2000, 50:511–516.PubMedCrossRef 2.