Florence Piette

Proteomics of life at low temperatures: trigger factor is the primary chaperone in the Antarctic bacterium Pseudoalteromonas haloplanktis TAC125.

The proteomes expressed at 4°C and 18°C by the psychrophilic Antarctic bacterium Pseudoalteromonas haloplanktis have been compared using two‐dimensional differential in‐gel electrophoresis, showing that translation, protein folding, membrane integrity and anti‐oxidant activities are upregulated at 4°C. This proteomic analysis revealed that the trigger factor is the main upregulated protein at low temperature. The trigger factor is the first molecular chaperone interacting with virtually all newly synthesized polypeptides on the ribosome and also possesses a peptidyl‐prolyl cis‐trans isomerase activity. This suggests that protein folding at low temperatures is a rate‐limiting step for bacterial growth in cold environments. It is proposed that the psychrophilic trigger factor rescues the chaperone function as both DnaK and GroEL (the major bacterial chaperones but also heat‐shock proteins) are downregulated at 4°C. The recombinant psychrophilic trigger factor is a monomer that displays unusually low conformational stability with a Tm value of 33°C, suggesting that the essential chaperone function requires considerable flexibility and dynamics to compensate for the reduction of molecular motions at freezing temperatures. Its chaperone activity is strongly temperature‐dependent and requires near‐zero temperature to stably bind a model‐unfolded polypeptide.

Life in the Cold: a Proteomic Study of Cold-Repressed Proteins in the Antarctic Bacterium Pseudoalteromonas haloplanktis TAC125

ABSTRACT The proteomes expressed at 4°C and 18°C by the psychrophilic Antarctic bacterium Pseudoalteromonas haloplanktis were compared using two-dimensional differential in-gel electrophoresis with special reference to proteins repressed by low temperatures. Remarkably, the major cold-repressed proteins, almost undetectable at 4°C, were heat shock proteins involved in folding assistance.

Fundamentals of Cold-Adapted Enzymes

The authors wish to thank N. Gerardin, A. Dernier and R. Marchand for their skilful technical assistance and the French Institute for Polar Research (IPEV – Institut Polaire Francais) for generously accommodating our research fellows at the French Antarctic station J.S. Dumont d’Urville in Terre Adelie. The generous support of the ‘Region Wallonne’ (contract FIRST EUROPE R0202/215266), the European Union (network contract CT970131) and the ‘Fonds National de la Recherche Scientifique’ is gratefully acknowledged. S D’Amico is a FNRS postdoctoral researcher. Frederic Roulling and Florence Piette are holders of a FRIA fellowship.

The protein folding challenge in psychrophiles: facts and current issues

The protein folding process in psychrophiles is impaired by low temperature, which exerts several physicochemical constraints, such as a decrease in the folding rate, reduced molecular diffusion rates and increased solvent viscosity, which interfere with conformational sampling. Furthermore, folding assistance is required at various folding steps according to the protein size. Recent studies in the field have provided contrasting and sometimes contradictory results, although protein folding generally appears as a rate-limiting step for the growth of psychrophiles. It is proposed here that these discrepancies reflect the diverse adaptive strategies adopted by psychrophiles in order to allow efficient protein folding at low temperature. Cold adaptations apparently superimpose on pre-existing cellular organization, resulting in different adaptive strategies. In addition, microbial lifestyle further modulates the properties of the chaperone machinery, which possibly explains the occurrence of cold-adapted and non-cold-adapted protein chaperones in psychrophiles.

Is there a cold shock response in the Antarctic psychrophile Pseudoalteromonas haloplanktis

The growth behavior and the proteomic response after a cold shock were investigated in the psychrophilic Antarctic bacterium Pseudoalteromonas haloplanktis. Remarkably, no cold-induced proteins were observed in the proteome, whereas some key proteins were repressed. This suggests noticeable differences in the cold shock response between a true psychrophile and mesophiles.

The Extreme Conditions of Life on the Planet and Exobiology

Extreme physicochemical conditions (low and high temperatures, high salinity, low and high pH, high hydrostatic pressure, etc.) existing on Earth are compatible with the occurrence of microbial life. The diversity and metabolic features of microbial trophic groups inhabiting extreme environments (cold, hot, saline, acidic, alkaline, and deep marine) are described. They include hydrothermal vents, acid springs, hypersaline and/or alkaline lakes, permafrost, and deep-sea environments, etc.