Secretion and Purification of Recombinant β1-4 Galactosyltransferase from Insect Cells Using pFmel-protA, a Novel Transposition-Based Baculovirus Transfer Vector

The palette of transfer vectors available for generation of recombinant baculoviruses based on transposition-mediated recombination has been enlarged by constructing the pFmel–protA vector. The pFmel–protA plasmid includes the honeybee melittin secretion signal and a Staphylococcus aureus protein A fusion protein tag, which allows the secretion and purification of recombinant proteins. Using this system, the human β1-4 galactosyltransferase-I protein was expressed in Sf9 insect cells at a level ranging from 22 to 28 U (4.8 to 6.0 mg)/L. The protein A tag enabled a simple monitoring of recombinant protein expression by enzyme-linked immunosorbent assay and Western blotting. Single step purification was achieved by immunoglobulin G affinity chromatography achieving a recovery yield of 28% and a specific activity of 1.9 U per mg of recombinant protein.