Role of H-1 and H-2 subunits of soybean seed ferritin in oxidative deposition of iron in protein.
Naturally occurring phytoferritin is a heteropolymer consisting of two different H-type subunits, H-1 and H-2. Prior to this study, however, the function of the two subunits in oxidative deposition of iron in ferritin was unknown. The data show that, upon aerobic addition of 48-200 Fe(2+)/shell to apoferritin, iron oxidation occurs only at the diiron ferroxidase center of recombinant H1 (rH-1). In addition to the diiron ferroxidase mechanism, such oxidation is catalyzed by the extension peptide (a specific domain found in phytoferritin) of rH-2, because the H-1 subunit is able to remove Fe(3+) from the center to the inner cavity better than the H-2 subunit. These findings support the idea that the H-1 and H-2 subunits play different roles in iron mineralization in protein. Interestingly, at medium iron loading (200 irons/shell), wild-type (WT) soybean seed ferritin (SSF) exhibits a stronger activity in catalyzing iron oxidation (1.10 ± 0.13 μm iron/subunit/s) than rH-1 (0.59 ± 0.07 μm iron/subunit/s) and rH-2 (0.48 ± 0.04 μm iron/subunit/s), demonstrating that a synergistic interaction exists between the H-1 and H-2 subunits in SSF during iron mineralization. Such synergistic interaction becomes considerably stronger at high iron loading (400 irons/shell) as indicated by the observation that the iron oxidation activity of WT SSF is ∼10 times larger than those of rH-1 and rH-2. This helps elucidate the widespread occurrence of heteropolymeric ferritins in plants.
Deng
Jianjun
J
CAU and ACC Joint Laboratory of Space Food, College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China.
Liao
Xiayun
X
Yang
Haixia
H
Zhang
Xiangyu
X
Hua
Zichun
Z
Masuda
Taro
T
Goto
Fumiyuki
F
Yoshihara
Toshihiro
T
Zhao
Guanghua
G
D000595:Amino Acid Sequence; D000818:Animals; D005293:Ferritins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D007501:Iron / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D013025:Glycine max / Q000737:chemistry / Q000378:metabolism*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
D021122:Protein Subunits; C030124:phytoferritin; D005293:Ferritins; D007501:Iron