Abstract
Although apoferritin has been widely utilized as a new class of natural protein nanovehicles for encapsulation and delivery of nutraceuticals, its ability to remove metal heavy ions has yet to be explored. In this study, for the first time, we demonstrated that the ferritin from kuruma prawns (Marsupenaeus japonicus), named MjF, has a pronouncedly larger ability to resist denaturation induced by Cd2+ and Hg2+ as compared to its analogue, human H-chain ferritin (HuHF), despite the fact that these two proteins share a high similarity in protein structure. Treatment of HuHF with Cd2+ or Hg2+ at a metal ion/protein shell ratio of 100/1 resulted in marked protein aggregation, while the MjF solution was kept constantly clear upon treatment with Cd2+ and Hg2+ at different protein shell/metal ion ratios (50/1, 100/1, 250/1, 500/1, 1000/1, and 2500/1). Structural comparison analyses in conjunction with the newly solved crystal structure of the complex of MjF plus Cd2+ or Hg2+ revealed that cysteine (Cys) is a major residue responsible for such binding, and that the large difference in the ability to resist denaturation induced by these two heavy metal ions between MjF and HuHF is mainly derived from the different positions of Cys residues in these two proteins; namely, Cys residues in HuHF are located on the outer surface, while Cys residues from MjF are buried within the protein shell. All of these findings raise the high possibility that prawn ferritin, as a food-derived protein, could be developed into a novel bio-template to remove heavy metal ions from contaminated food systems.
Highlights
Heavy metal ion contamination has become one of the most serious environmental problems in recent years and is closely related to food safety because of their nonbiodegradable and accumulated characters
We demonstrated that Marsupenaeus japonicus ferritin (MjF) exhibits a markedly higher binding capacity to heavy metal ions such as Cd2+ and Hg2+ as compared to human H-chain ferritin (HuHF), they share high structural similarity in protein structure
The present study provides a foundation for developing a biological material for the removal of heavy metal ions, which might be utilized in food and other related industries
Summary
Heavy metal ion contamination has become one of the most serious environmental problems in recent years and is closely related to food safety because of their nonbiodegradable and accumulated characters. Since heavy metal ions are the most widespread and harmful contaminants, there are numerous available technologies for water purification and heavy metal ion elimination These technologies can be divided into chemical and biological methods. Chemical methods include adsorption [4], ion-exchange [5], precipitation [6], membrane filtration (microfiltration, nanofiltration, and ultrafiltration), and electrochemical detection [6,7,8]. The bio-absorption of heavy metals from drinking water and foods is a relatively new technique that has been shown to be promising for the removal of heavy metal ions [5,9,10] Biological materials with such activities include eggshell-membrane [11], polyacrylic hydrogel [12], and biochars [13]. Despite these materials having effective adsorption and an inexpensive price, they have rarely been developed to detect and remove the heavy metal ions in beverages and milk [14,15] because it is difficult to remove the heavy metal ions without impairing their nutritive contents
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