Stress regulation of the PAN–proteasome system in the extreme halophilic archaeon Halobacterium

• Published in: Extremophiles : life under extreme conditions 2012-03, Vol.16 (2), p.215-225
• Main Authors: Chamieh, H., Marty, V., Guetta, D., Perollier, A., Franzetti, B.
• Format: Article
• Language: English
• Subjects: Adenosine Triphosphatases - chemistry; Adenosinetriphosphatase; Animal, plant and microbial ecology; Archaea; Biochemistry; Biodegradation; Biological and medical sciences; Biomedical and Life Sciences; Biotechnology; Cell culture; Cellular biology; Centrifugation, Density Gradient; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Archaeal; Gene regulation; Growth conditions; Halobacterium; Halobacterium salinarum - genetics; Halobacterium salinarum - metabolism; Halophiles; Heat shock; Hot Temperature; Immunoprecipitation; Life Sciences; Microbial Ecology; Microbiology; Mortality; Nucleotidases - chemistry; Original Paper; peptidase; Peptide Hydrolases - chemistry; Proteases; Proteasome Endopeptidase Complex - metabolism; proteasomes; Proteinase; Proteolysis; Salinity; Salts; Salts - chemistry; Space life sciences; Stress; Sucrose - chemistry; Time Factors; Transcription; Transcription, Genetic; Ultracentrifugation; vinyl sulfone
• ISSN: 1431-0651; 1433-4909
• DOI: 10.1007/s00792-011-0421-0

In Archaea, the importance of the proteasome system for basic biological processes is only poorly understood. Proteasomes were partially purified from Halobacterium by native gradient density ultracentrifugation. The peptidase activity profiles showed that the 20S proteasome accumulation is altered depending on the physiological state of the cells. The amount of active 20S particles increases in Halobacterium cells as a response to thermal and low salt stresses. In the same conditions, Northern experiments showed a positive transcriptional regulation of the alpha and beta proteasome subunits as well as of the two proteasome regulatory ATPases, PANA and PANB. Co-immunoprecipitation experiments demonstrated the existence of a physical interaction between the two P roteasome A ctivating N ucleotidase (PAN) proteins in cell extracts. Thus, a direct regulation occurs on the PAN–proteasome components to adjust the protein degradation activity to growth and environmental constraints. These results also indicate that, in extreme halophiles, proteasome mediated proteolysis is an important aspect of low salt stress response. The tri-peptide vinyl sulfone inhibitor NLVS was used in cell cultures to study the in vivo function of proteasome in Halobacterium. The chemical inhibition of proteasomes was measured in the cellular extracts. It has no effect on cell growth and mortality under normal growth conditions as well as under heat shock conditions. These results suggest that the PAN activators or other proteases compensate for loss of proteasome activity in stress conditions.