A Novel Metal Adsorbent Composed of a Hexa-histidine Tag and a Carbohydrate-binding Module on Cellulose

We developed a novel metal adsorbent composed of bio-based materials, cellulose and a protein. The approach involved the immobilization of a hexa-histidine tag (His6), which shows an affinity for an intermediate acid (metal ion) in Hard and Soft Acids and Bases (HSAB) theory, on cellulose by fusing with a carbohydrate-binding module (CBM). The results show that CBM-His6-bound cellulose has adsorption selectivity reflecting the original properties of His6. Additionally, we prepared three configurations of CBM-His6 proteins, which were subsequently immobilized on filter paper for Ni2+ ion adsorption. Of these configurations, we found that the protein containing two His6 tags at each terminus (N– and C–) of CBM exhibited the highest metal adsorption ability. Furthermore, XPS analysis confirmed the binding of Ni2+ ions on the cellulose.