title: Expression, purification, and characterization of recombinant gamma-carboxylated factor IX synthesized in Chinese hamster ovary cells.
abstract: Factor IX has been expressed to high levels within a recombinant host cell and the biologically active fraction subsequently purified to homogeneity for characterization. The coding sequence for Factor IX was inserted into a mammalian cell expression vector and transfected into dihydrofolate reductase-deficient Chinese hamster ovary cells. The integrated DNA was amplified to a high copy number by selection for increasingly higher expression levels of the marker gene, dihydrofolate reductase, contained within a co-transfected plasmid. Cloned cell lines secreting over 100 micrograms/ml Factor IX antigen and up to 1.5 microgram/ml native Factor IX antigen have been obtained. Expression of biologically active Factor IX was dependent on the presence of vitamin K in the culture media. The gamma-carboxylated Factor IX was isolated from cell culture fluid by immunoaffinity chromatography using antibodies conformation-specific for the metal-stabilized conformer of Factor IX. This conformation is dependent upon metal ions and gamma-carboxyglutamic acid. Purified recombinant Factor IX migrated as a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis with an electrophoretic mobility equivalent to plasma-derived Factor IX. The purified recombinant Factor IX demonstrated Factor IX coagulant activity, measured in Factor IX-deficient plasma, of 35-75 units/mg. Amino acid analysis of the alkaline hydrolysate of recombinant Factor IX demonstrated an average of 6-7 mol of gamma-carboxyglutamic acid per mol of Factor IX. NH2-terminal sequence analysis of the first 17 residues revealed equivalent amino acid sequences for both purified recombinant and plasma-derived Factor IX. The results represent the first purification and characterization of a biologically active, gamma-carboxylated vitamin K-dependent protein expressed in a recombinant DNA system.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D002999:Clone Cells / Q000032:analysis; D006224:Cricetinae; D003412:Cricetulus; D004591:Electrophoresis, Polyacrylamide Gel; D005164:Factor IX / Q000096:biosynthesis / Q000235:genetics* / Q000302:isolation & purification; D005260:Female; D005786:Gene Expression Regulation; D008727:Methotrexate / Q000494:pharmacology; D010957:Plasmids; D011994:Recombinant Proteins / Q000302:isolation & purification*; D010837:Vitamin K 1 / Q000494:pharmacology
chemical_list: D011994:Recombinant Proteins; D010837:Vitamin K 1; D005164:Factor IX; D008727:Methotrexate