RESUMO
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.
Assuntos
Proteínas de Bactérias/metabolismo , Resposta ao Choque Frio/fisiologia , Proteoma/metabolismo , Pseudoalteromonas/metabolismo , Regiões AntárticasRESUMO
The proteomes expressed at 4 degrees C and 18 degrees 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 degrees 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 degrees C. The recombinant psychrophilic trigger factor is a monomer that displays unusually low conformational stability with a Tm value of 33 degrees 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.
Assuntos
Proteínas de Bactérias/análise , Temperatura Baixa , Chaperonas Moleculares/biossíntese , Peptidilprolil Isomerase/biossíntese , Proteoma/análise , Pseudoalteromonas/química , Pseudoalteromonas/efeitos da radiação , Eletroforese em Gel Bidimensional , Cinética , Chaperonas Moleculares/química , Chaperonas Moleculares/isolamento & purificação , Peptidilprolil Isomerase/química , Peptidilprolil Isomerase/isolamento & purificação , Estabilidade Proteica , Proteínas Recombinantes/química , Proteínas Recombinantes/isolamento & purificaçãoRESUMO
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.
Assuntos
Archaea/fisiologia , Fenômenos Fisiológicos Bacterianos , Temperatura Baixa , Dobramento de Proteína , Adaptação Fisiológica , Archaea/metabolismo , Regulação da Expressão Gênica em Archaea , Regulação Bacteriana da Expressão Gênica , Chaperonas Moleculares/metabolismo , Biossíntese de ProteínasRESUMO
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.