Abstract: Objective: To construct the expression vector of the fusion protein of human serum albumin (HSA) and thymopentin (TP5) and to express it in Pichia pastoris, and to elucidate the biological activity of fusion protein. Methods: The HSA-TP5 fusion gene was constructed by gene recombination and transfected into Pichia pastoris to construct the eukaryotic expression system of HSA-TP5. The recombinant eukaryotic expression plasmid of PPICZα -HSA-TP5 was obtained by agarose gel electrophoresis and purification reagent. The two step fermentation method was used to ferment gene engineering bacteria of HSA-TP5 in high density, and the fermentation supernatant protein was precipitated and concentrated; the purified fusion protein was obtained by cation exchange chromatography and hydrophobic chromatography and analyzed by SDS-polyacrylamide gel electrophoresis. The effect of the fusion protein on the proliferation of lymphocytes was detected by MTT assay. Results: The HSA target gene fragment with length of 1 845 bp was achieved by PCR method. The HSA-TP5-pPICZαC fusion plasmid was identified by restriction endonuclease digestion, and the fragment length was 707 bp. The sequence analysis showed that the HSA and TP5 sequences of the target genes were identical with the gene sequences reported in GenBank and were fused by forward fusion. PCR method confirmed that the eukaryotic recombinant plasmid PPICZ αC -HSA-TP5 was integrated into the yeast genome, and compared with control group, the target gene PCR product length was found to be 1 860 bp. SDS-PAGE analysis showed that the expression level of HSA-TP5 fusion protein was gradually increased with the induction time within 72 h. HSA-TP5 fusion protein was purified by cation exchange chromatography and AKTA multifunctional protein purification system.The MTT assay results showed that HSA-TP5 fusion protein was consistent with TP5 protein in promoting lymphocyte proliferation activity. Conclusion: HSA-TP5 fusion protein can be obtained by constructing the eukaryotic expression system of Pichia pastoris and owns the biological activity.

Key words: thymopentin, human serum albumin, fusion gene, gene expression