tailieunhanh - Báo cáo khoa học: Comparative studies of endonuclease I from cold-adapted Vibrio salmonicida and mesophilic Vibrio cholerae

Endonuclease I is a periplasmic or extracellular enzyme present in many different Proteobacteria. TheendAgene encoding endonuclease I from the psychrophilic and mildly halophilic bacteriumVibrio salmonicidaand from the mesophilic brackish water bacterium Vibrio choleraehave been cloned, over-expressed inEscherichia coli, and purified. | ễFEBS Journal Comparative studies of endonuclease I from cold-adapted Vibrio salmonicida and mesophilic Vibrio cholerae Bj0rn Altermark1 Laila Niiranen2 Nils P. Willassen1 2 Arne O. Smalas1 and Elin Moe1 1 Norwegian StructuralBiology Centre Faculty of Science University of Tromso Norway 2 Department of Molecular Biotechnology Faculty of Medicine University of Tromso Norway Keywords cold adaptation endonuclease I psychrophilic enzymes salt adaptation stability Correspondence E. Moe Norwegian StructuralBiology Centre Faculty of Science University of Tromso N-9037 Tromso Norway Fax 47 77644765 Tel 47 77646473 E-mail Received 14 September 2006 revised 2 November 2006 accepted 9 November 2006 doi Endonuclease I is a periplasmic or extracellular enzyme present in many different Proteobacteria. The endA gene encoding endonuclease I from the psychrophilic and mildly halophilic bacterium Vibrio salmonicida and from the mesophilic brackish water bacterium Vibrio cholerae have been cloned over-expressed in Escherichia coli and purified. A comparison of the enzymatic properties shows large differences in NaCl requirements optimum pH temperature stability and catalytic efficiency of the two proteins. The V. salmonicida EndA shows typical cold-adapted features such as lower unfolding temperature lower temperature optimum for activity and higher specific activity than V. cholerae EndA. The thermodynamic activation parameters confirm the psychrophilic nature of V. salmonicida EndA with a much lower activation enthalpy. The optimal conditions for enzymatic activity coincide well with the corresponding optimal requirements for growth of the organisms and the enzymes function predominantly as DNases at physiological concentrations of NaCl. The periplasmic or extracellular localization of the enzymes which renders them constantly exposed to the outer environment of the cell may explain this fine-tuning of biochemical properties. .