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.