Enhancing Soluble Expression and Post-Translational Modification of Mussel Foot Protein in E. coli

Due to intrinsically low solubility and stability, recombinant mussel foot proteins (Mfps) require an efficient system that supports large-scale production of dopanized-Mfps. Here, we engineered a 39-aa peptide tag, termed T7B9M3, to increase the solubility of Mfps in Escherichia coli. The absence of net charged residues, rather than the copy number or the predicted α-helical structure of the T7B9M3 tag, contributes to the solubility enhancement. T7B9M3-fp-3B achieved a 365.96 mg/L soluble protein titer with a 98.75% soluble rate in a shake flask. Coupling the tyrosinase coexpression to endow Mfps with a dopaminization capability, the tyrosine hydroxylation efficiency reached 19.82%. Moreover, dopanized-Mfps tended to form stronger interactions with various substrates, including glass, polypropylene, and polyethylene, than the unmodified version. Our findings suggest that the combined strategy may contribute to establishing a scalable and low-cost protein expression platform with the potential for batch production of functional Mfps.