EXPRESSION OF ACTIVE, SECRETED HUMAN PROSTATE-SPECIFIC ANTIGEN BY RECOMBINANT BACULOVIRUS-INFECTED INSECT CELLS ON A PILOT-SCALE

We have expressed human prostate-specific antigen (PSA) on a pilot-sca le in Spodoptera frugiperda Sf9 insect cells using recombinant baculov irus system, Infected cells secreted PSA into culture medium at a conc entration of 2-4 mg per liter. PSA was expressed both in active and in active forms which were separated in a final purification step using c ation-exchange chromatography eluted with a low salt gradient, The N-t erminus of active PSA was correctly cleaved; two amino acids of the pr opeptide remained, however, at the N-terminus of the inactive PSA. Pur ified recombinant PSA showed a chymotrypsin-like activity with the syn thetic substrate MeO-Suc-Arg-Pro-Tyr-pNA, but did not have a trypsin-l ike activity when Pro-Phe-Arg-pNA was used. The molecular mass of acti ve PSA was 31.0 kDa in reduced SDS-PAGE, 26.0 kDa in nonreduced SDS-PA GE and 26.5 kDa in ion spray mass spectrometry. The active protein for med complexes with alpha(1)-antichymotrypsin (ACT) and alpha(2)-macrog lobulin (alpha(2)M) ill vitro similar to the commercial PSA purified f rom human seminal fluid.