Co-Immobilization of Xylanase and Scaffolding Protein onto an Immobilized Metal Ion Affinity Membrane

Lignocellulosic biomass conversion technology seeks to convert agricultural waste to sugars through the use of various cellulases and hemicellulases. In practice, the application of free enzymes might increase the cost of the process due to difficulties with recovery of the enzymes and products. Immobilization might be an effective approach for recovering the hydrolysis products and improving the stability and reusability of the enzymes. In this study, we used a recombinant genetic engineering approach to construct a scaffold protein gene (CipA) and a xylanase gene (XynC) fused to a dockerin gene (DocT). After expressing CipA and XynC-DocT (XynCt) genes using E. coli hosts, the crude extracts were collected. An immobilized metal ion affinity membrane/Co2+ ion (IMAM-Co2+) system was prepared to adsorb CipA in its crude extract, thereby allowing simultaneous purification and immobilization of CipA protein. A similar approach was applied for the adsorption of XynCt protein, exploiting the interaction between the cohesin units in IMAM-Co2+-CipA and the dockerin unit in XynCt. The activity of the xylanase unit was enhanced in the presence of Co2+ for both the free XynCt enzymes and the immobilized CipA-XynCt. The heat resistance and stability over a wide range of values of pH of the immobilized CipA-XynCt were superior to those of the free XynCt. Furthermore, the immobilized CipA-XynCt retained approximately 80% of its initial activity after seven reaction cycles. The values of Km and νmax of IMAM-Co2+-CipA-XynCt (1.513 mg/mL and 3.831 U/mg, respectively) were the best among those of the other tested forms of XynCt.