Purification of metallothionein proteins from the crab, Portunus pelagicus-selectivity of hydrophobic interaction chromatography

Both hydrophobic interaction chromatography (HIC) and ion-exchange chromatography (IEC) are commonly used for the purification of proteins as their mild elution conditions preclude the dangers of denaturation. Of the two methods, IEC which fractionates proteins on the basis of charge differences, exhibits a higher selectivity. In the case of the metallothionein (MT) proteins, the charge states of the proteins are very susceptible to change due to oxidation of the abundant thiol groups. This complicates fractionation with IEC. Separation using HIC, on the other hand, is based on the exposed hydrophobic groups, which remain relatively intact if the tertiary structure of the proteins is not disrupted. In this work, the successful isolation of two MT isoforms from the tropical crab species, Portunus pelagicus, using HIC serves to demonstrate the high selectivity of this technique, in addition to the fact that it is indifferent to the state of oxidation of the MT proteins during the purification procedure.