Soluble Expression of Recombinant Human BMP6 in Escherichia coli and Its Purification and Bioassay in vitro

BMP6 is a potent protein for future treatment strategies of bone regeneration as it is a very important regulator of bone homeostasis. Active BMP6 is a dimer containing multidisulfide bonds and is a highly hydrophobic protein prone to aggregation. To obtain soluble and active BMP6 in Escherichia coli, the effects of four N-terminal fusion tags (TRX, GST, MBP and CBD) and N-terminal His-tag were compared. The expression and solubility were tested under different conditions (expression hosts, temperatures and inductor concentrations). A series of experiments led to the finding that the placement of MBP before the BMP6 was best in availing the soluble expression of the protein. It was also found that in E. coli BL21trxB (DE3) cytoplasm, which is a thioredoxin reductase mutant strain, soluble homodimeric BMP6 can be formed. The overexpressed MBP-BMP6 fusion protein was purified and shown to be functionally active.