Iron in phytoferritin from legume seeds is required for seedling germination and early growth. However, the mechanism by which phytoferritin regulates its iron complement to these physiological processes remains unknown. In the present study, protein degradation is found to occur in purified SSF (soya bean seed ferritin) (consisting of H-1 and H-2 subunits) during storage, consistent with previous results that such degradation also occurs during seedling germination. In contrast, no degradation is observed with animal ferritin under identical conditions, suggesting that SSF autodegradation might be due to the EP (extension peptide) on the exterior surface of the protein, a specific domain found only in phytoferritin. Indeed, EP-deleted SSF becomes stable, confirming the above hypothesis. Further support comes from a protease activity assay showing that EP-1 (corresponding to the EP of the H-1 subunit) exhibits significant serine protease-like activity, whereas the activity of EP-2 (corresponding to the EP of the H-2 subunit) is much weaker. Consistent with the observation above, rH-1 (recombinant H-1 ferritin) is prone to degradation, whereas its analogue, rH-2, becomes very stable under identical conditions. This demonstrates that SSF degradation mainly originates from the serine protease-like activity of EP-1. Associated with EP degradation is a considerable increase in the rate of iron release from SSF induced by ascorbate in the amyloplast (pH range, 5.8–6.1). Thus phytoferritin may have facilitated the evolution of the specific domain to control its iron complement in response to cell iron need in the seedling stage.
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Research Article|
March 29 2010
A novel EP-involved pathway for iron release from soya bean seed ferritin
Xiaoping Fu
;
Xiaoping Fu
*
CAU and ACC Joint Laboratory of Space Food, College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China
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Jianjun Deng
;
Jianjun Deng
*
CAU and ACC Joint Laboratory of Space Food, College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China
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Haixia Yang
;
Haixia Yang
*
CAU and ACC Joint Laboratory of Space Food, College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China
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Taro Masuda
;
Taro Masuda
†
Laboratory of Food Quality Design and Development, Division of Agronomy and Horticultural Science, Graduate School of Agriculture, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan
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Fumiyuki Goto
;
Fumiyuki Goto
‡
Biotechnology Sector, Environmental Science Research Laboratory, Central Research Institute of Electric Power Industry, 1646 Abiko, Chiba 270-1194, Japan
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Toshihiro Yoshihara
;
Toshihiro Yoshihara
‡
Biotechnology Sector, Environmental Science Research Laboratory, Central Research Institute of Electric Power Industry, 1646 Abiko, Chiba 270-1194, Japan
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Guanghua Zhao
Guanghua Zhao
1
*
CAU and ACC Joint Laboratory of Space Food, College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China1
To whom correspondence should be addressed (email gzhao1000@yahoo.com).
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Biochem J (2010) 427 (2): 313-321.
Article history
Received:
January 04 2010
Revision Received:
February 08 2010
Accepted:
February 10 2010
Accepted Manuscript online:
February 10 2010
Citation
Xiaoping Fu, Jianjun Deng, Haixia Yang, Taro Masuda, Fumiyuki Goto, Toshihiro Yoshihara, Guanghua Zhao; A novel EP-involved pathway for iron release from soya bean seed ferritin. Biochem J 15 April 2010; 427 (2): 313–321. doi: https://doi.org/10.1042/BJ20100015
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