Effects of His-Tag Length on the Soluble Expression and Selective Immobilization of D-Amino Acid Oxidase from Trigonopsis variabilis: A Preliminary Study

His-tags are widely used for the purification of recombinant proteins. High-cost carriers functionalized with nickel ions are commonly required for the selective immobilization of His-tagged enzymes. In this study, His-tags of varying lengths were fused to the N-terminus of D-amino acid oxidase (DAO) from Trigonopsis variabilis. The attachment of a His6 tag significantly improved the solubility of the recombinant DAO expressed in Escherichia coli. By modulating the tag lengths, a better balance between cell growth and protein solubility was achieved, resulting in a higher volume activity (His3). Furthermore, the fusion of longer tags (His6 and His9) facilitated the rapid immobilization of DAOs onto a commercial epoxy carrier without metal bearing, resulting in more selective immobilization. In conclusion, the modulation of His-tag length was preliminarily demonstrated as a simple and cost-effective approach to achieve efficient expression, as well as fast and selective immobilization of DAO.