Purification and characterization of Cop, a protein involved in the copy number control of plasmid pE194

  • Jin-Hwan Kwak
  • Jungho Kim
  • Mu-Yong Kim
  • Eung-Chil Choi
Research Articles


Cop protein has been overexpressed inEscherichia coli using a T7 RNA polymerase system. Purification to apparent homogeneity was achieved by the sequential chromatography on ion exchange, affinity chromatography, and reverse phase high performance liquid chromatography system. The molecular weight of the purified Cop was estimated as 6.1 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). But the molecular mass of the native state Cop was shown to be 19 kDa by an analytical high performance size exclusion chromatography, suggesting a trimer-like structure in 50 mM Tris-HCI buffer (pH 7.5) containing 100 mM NaCl. Cop protein was calculated to contain 39.1% α-helix, 16.8% β-sheet, 17.4% turn, and 26.8% random structure. The DNA binding property of Cop protein expressed inE. coli was preserved during the expression and purification process. The isoelectric point of Cop was determined to be 9.0. The results of amino acid composition analysis and N-terminal amino acid sequencing of Cop showed that it has the same amino acid composition and N-terminal amino acid sequence as those deduced from its DNA sequence analysis, except for the partial removal of N-terminal methionine residue by methionyl-aminopeptidase inE. coli.

Key words

Cop protein pE194 Isoelectric point N-terminal sequencing Circular dichroism spectrum 

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Copyright information

© The Pharmaceutical Society of Korea 1998

Authors and Affiliations

  • Jin-Hwan Kwak
    • 4
  • Jungho Kim
    • 1
  • Mu-Yong Kim
    • 2
  • Eung-Chil Choi
    • 3
  1. 1.Department of BiochemistryMcGill UniversityMontrealCanada
  2. 2.LG Chem Research ParkLG Chemical Ltd.TaejonKorea
  3. 3.College of PharmacySeoul National UniversitySeoulKorea
  4. 4.School of Bioscience and Food TechnologyHandong UniversityPohangKorea

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