US EPA

3811617 

Journal Article 

Heme-mediated binding of α-casein to ferritin: evidence for preferential α-casein binding to ferrous iron 

Usami, A; Tanaka, M; Yoshikawa, Y; Watanabe, K; Ohtsuka, H; Orino, K 

2011 

Yes 

BioMetals
ISSN: 0966-0844
EISSN: 1572-8773 

24 

6 

1217-1224 

English 

21732136 

10.1007/s10534-011-9470-1 

WOS:000297117100022 

Bovine milk α-casein was identified as a ferritin-binding protein, and ferritin is known to be a heme-binding protein. In this study, we found that the binding of α-casein to bovine spleen ferritin in vitro was blocked by hemin, but not by iron-free hemin (protoporphyrin IX) or zinc-protoporphyrin IX, suggesting that the presence of iron in heme play a key role in this interaction. Indeed, the binding of α-casein to ferritin and biotinylated hemin was inhibited by adding excess ferrous ammonium sulfate (FAS). To further elucidate the binding mechanism of α-casein to biotinylated hemin, Ferrozine and nitrilotriacetic acid (NTA) were used as ferrous and ferric iron chelators, respectively. FAS-mediated inhibition of α-casein to biotinylated hemin was neutralized with Ferrozine, but not NTA, while FAS- as well as ferric chloride-mediated inhibition in their interaction was neutralized by NTA. The following ions also inhibited α-casein-biotinylated hemin binding in order of potency of inhibition: FAS (Fe(2+)) < ferric chloride (Fe(3+)) < copper sulfate (Cu(2+)) < zinc sulfate (Zn(2+)) < manganese chloride (Mn(2+)) < calcium chloride (Ca(2+)) < magnesium sulfate (Mg(2+)). These results suggests that the binding of α-casein to ferritin is heme-mediated through direct binding of α-casein to iron in the heme on the surface of ferritin molecule, and that α-casein preferentially binds Fe(2+) compared with any other metal ions, including Fe(3+).