Structure,Function, and Nutrition of Phytoferritin: A Newly Functional Factor for Iron Supplement

Ferritins are members of the superfamily of iron storage and detoxification proteins present in all living organisms and play important roles in controlling cellular iron homeostasis. In contrast to animal ferritin, relatively little information is available on the structure and function of phytoferritin. Phytoferritin is observed in plastids whereas animal ferritins are largely found in the cytoplasm of cell. Compared to animal ferritin, phytoferritin exhibits two major distinctive features in structure. First, phytoferritin contains a specific extension peptide (EP) at the N-terminal while animal ferritin lacks it. The EP is located on the exterior surface of protein, which recently has been found to act as a second ferroxidase center for iron-binding and oxidation, and regulate iron release during the germination and early growth of seedlings. Second, only H-type subunit has been identified in phytoferritin, which is usually a heteropolymer consisting of two different subunits, H-1 and H-2, sharing ～80% amino acid sequence identity. These two subunits in phytoferritin play a positively cooperative role in iron oxidative deposition in protein. Iron deficiency anemia (IDA) is the most common and widespread nutritional disorder in the world, so it is crucial to explore a safe and efficient functional factor for iron supplement. Fortunately, phytoferritin seems to be a suitable candidate. In legume seeds, more than 90% of iron is stored in the form of ferritin in amyloplasts. Recently, some studies at different levels have demonstrated that plant ferritin could be used as novel, utilizable, plant-based forms of iron for populations with a low iron status. This review focuses on recent progress in structure, function, and nutrition of phytoferritin.