Melanin, a potential new matrix material for recombinant His-tag protein purification

Abstract

Nickel-Sepharose (Ni-Sepharose) has been being applied as the most common matrix in purifying His-tag proteins based on the affinity interaction between histidine residues and Ni2+ ion. However, Sepharose still comes at high cost for this purification purpose, especially in developing countries as Vietnam. Here, we show for the first time that melanin from ink sacs of squids which is considered as biowaste in the food industry, can be used as a new potential matrix material instead of Sepharose. We utilized either melanin or melanin charged with metal ions as the stationary phase of affinity purification of His-tag proteins. The results showed that a recombinant His-tag protein VP28 in a protein pool was captured by melanin and Ni2+/Fe3+/Zn2+ chelated melanin. Experiments for releasing VP28 were performed only on the melanin and Ni2+-melanin matrices. The result showed that VP28 was quite selectively eluted when applying elution buffer of 250 mM imidazole overnight. The relative efficiency in releasing VP28 of melanin and Ni-melanin matrices roughly compared to Ni-Sepharose were about 38 and 18% respectively. Further optimization of this process may allow higher efficiency in the purification of His-tag proteins.