Expression of codon optimized human bone morphogenetic protein 4 in Pichia pastoris

Bone morphogenetic proteins (BMPs) are TGF-β family member proteins that have therapeutic potential. The amount of BMPs from natural resources is limited, and the production of biologically active BMPs in heterologous protein expression systems remains an obstacle for their clinical application. In this study, the DNA sequence of human BMP4 mature domain (hBMP4) was optimized according to the codon relative synonymous codon usage values in Pichia pastoris, and the A+T content in the sequence after optimization was within the range of 30% to 55%. In Pichia pastoris cultured in shake-flask, the expression level of hBMP4 protein from the optimized sequence (48 mg/L) increased fourfold in comparison with that from the native sequence (12 mg/L). Recombinant hBMP4 protein was purified by SP Sepharose and heparin affinity chromatography. The biological activities of recombinant hBMP4 were examined by measuring proliferation stimulation in cells and induction of ectopic cartilage formation in mouse models. Our results demonstrated that the optimized DNA sequence could significantly enhance hBMP4 protein expression in Pichia pastoris compared with the native sequence and produce biologically active recombinant hBMP4; this indicates the potential of this optimized sequence for bulk production of hBMP4 protein in future clinical applications.