Possible involvement of an FKBP family member protein from a psychrotrophic bacterium Shewanella sp. SIB1 in cold-adaptation

Authors


  • Enzymes: peptidyl-prolyl cis-trans isomerase (PPIases, EC 5.2.1.8).

  • Note: The nucleotide sequence reported in this paper has been deposited in DDBJ with accession number AB116100.

S. Kanaya, Department of Material and Life Science, Graduate School of Engineering, Osaka University, 2–1, Yamadaoka, Suita, Osaka 565–0871, Japan.
Fax/Tel.: + 81 6 6879 7938; E-mail: kanaya@mls.eng.osaka-u.ac.jp

Abstract

A psychrotrophic bacterium Shewanella sp. strain SIB1 was grown at 4 and 20 °C, and total soluble proteins extracted from the cells were analyzed by two-dimensional polyacrylamide gel electrophoresis. Comparison of these patterns showed that the cellular content of a protein with a molecular mass of 28 kDa and an isoelectric point of four greatly increased at 4 °C compared to that at 20 °C. Determination of the N-terminal amino acid sequence, followed by the cloning and sequencing of the gene encoding this protein, revealed that this protein is a member of the FKBP family of proteins with an amino acid sequence identity of 56% to Escherichia coli FKBP22. This protein was overproduced in E. coli in a His-tagged form, purified, and analyzed for peptidyl-prolyl cis-trans isomerase activity. When this activity was determined by the protease coupling assay using N-succinyl-Ala-Leu-Pro-Phe-p-nitroanilide as a substrate at various temperatures, the protein exhibited the highest activity at 10 °C with a kcat/Km value of 0.87 µm−1·s−1. When the peptidyl-prolyl cis-trans isomerase activity was determined by the RNase T1 refolding assay at 10 and 20 °C, the protein exhibited higher activity at 10 °C with a kcat/Km value of 0.50 µm−1·s−1. These kcat/Km values are lower but comparable to those of E. coli FKBP22. We propose that a FKBP family protein is involved in cold-adaptation of psychrotrophic bacteria.

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