OBJECTIVETo construct the prokaryotic expression plasmid pET15b-PEP-1-CAT to obtain purified fusion protein of PEP-1-CAT.

METHODSUsing pfu DNA polymerase, the full-length human catalase cDNA was amplified by PCR from pZeoSV2(+)-CAT plasmid, and the PCR product was added with "A" using Taq DNA polymerase. The purified product of CAT cDNA with the base A at its 3' end was ligated with pGEM-T Easy vector and transformed into DH5alpha. The correct recombinant was identified by PCR and Sal I/Bgl II digestion and named as pGEM-T-CAT. Two oligonucleotides were synthesized and annealed to generate a double-stranded oligonucleotide encoding the PEP-1 peptide, which was directly ligated into Nde I/Xho I-digested pET15b. The recombinant plasmid was identified by double-enzyme digestion and named as pET15b-PEP-1. pET15b-PEP-1 and pGEM-T-CAT were further digested by Xho I/BamH I and Sal I/Bgl II, respectively. The purified linear fragment of pET15b-PEP-1 and CAT cDNA fragment were ligated using two pairs of isocaudarners possessing different recognition sequences but producing compatible cohesive ends. The clone with the expected insert was selected using Xho I restriction analysis followed by sequence analysis. The recombinant plasmid was transformed into E. coli BL21(DE3) which was induced by IPTG. The recombinant protein possessed an N-terminal His-tag sequence which could be used to purify the target protein by affinity chromatography on a Ni(2+)-NTA-resin column. The fusion protein PEP-1-CAT was produced and confirmed by specific enzyme activity in vitro.

RESULTSSequence analysis showed that the PEP-1 and the human CAT cDNA sequence of pET15b- PEP-1-CAT had identical sequence with designed PEP-1 peptide and human catalase cDNA sequence in GenBank (accession No. AY028632), respectively. SDS-PAGE and Western blotting confirmed successful expression and purification of PEP-1-CAT fusion protein with specific activity of 77.15 U/g.

CONCLUSIONThe prokaryotic expression plasmid pET15b-PEP-1-CAT has been constructed successfully, and the successful expression and purification of PEP-1-CAT provides a basis for prevention and therapy of various disorders related to oxidative stress.