A Novel H-NS-like protein from an antarctic psychrophilic bacterium reveals a crucial role for the N-terminal domain in thermal stability

• Published in: Journal of Biological Chemistry
• Main Authors: Soutourina, OA, Danchin, A, Bertin, PN, Tendeng, C, Krin, E, Marin, A
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Society for Biochemistry and Molecular Biology, Inc. The Journal's web site is located at http://www.jbc.org/ 2003
• Subjects: Acinetobacter - chemistry; Bacterial Proteins - chemistry - metabolism; DNA-Binding Proteins - chemistry - metabolism; Gammaproteobacteria - chemistry; Rhodobacter capsulatus - chemistry; Antarctic; Antarc*; Antarctica; Siberia
• Online Access: https://doi.org/10.1074/jbc.M211766200; http://hdl.handle.net/10722/225141

We describe here new members of the H-NS protein family identified in a psychrotrophic Acinetobacter spp. bacterium collected in Siberia and in a psychrophilic Psychrobacter spp. bacterium collected in Antarctica. Both are phylogenetically closely related to the HvrA and SPB Rhodobacter transcriptional regulators. Their amino acid sequence shares 40% identity, and their predicted secondary structure displays a structural and functional organization in two modules similar to that of H-NS in Escherichia coli. Remarkably, the Acinetobacter protein fully restores to the wild-type H-NS-dependent phenotypes, whereas the Psychrobacter protein is no longer able to reverse the effects of H-NS deficiency in an E. coli mutant strain above 30 degrees C. Moreover, in vitro experiments demonstrate that the ability of the Psychrobacter H-NS protein to bind curved DNA and to form dimers is altered at 37 degrees C. The construction of hybrid proteins containing the N- or the C-terminal part of E. coli H-NS fused to the C- or N-terminal part of the Psychrobacter protein demonstrates the role of the N-terminal domain in this process. Finally, circular dichroism analysis of purified H-NS proteins suggests that, as compared with the E. coli and Acinetobacter proteins, the alpha-helical domain displays weaker intermolecular interactions in the Psychrobacter protein, which may account for the low thermal stability observed at 37 degrees C.