標題: Evidence for beta-lactoglobulin involvement in vitamin D transport in vivo- role of the gamma-turn (Leu-Pro-Met) of beta-lactoglobulin in vitamin D binding
作者: Yang, Ming Chi
Chen, Nai Chi
Chen, Chun-Jung
Wu, Chin Yun
Mao, Simon J. T.
生醫工程研究所
Institute of Biomedical Engineering
關鍵字: beta-lactoglobulin;monoclonal antibody;site-directed mutagenesis;vitamin D binding;vitamin D transport and uptake
公開日期: 1-Apr-2009
摘要: beta-lactoglobulin (LG) is a major bovine milk protein, containing a central calyx and a second exosite beyond the calyx to bind vitamin D; however, the biological function of LG in transporting vitamin D remains elusive. Crystallographic findings from our previous study showed the exosite to be located at the pocket between the alpha-helix and beta-strand I. In the present study, using site-directed mutagenesis, we demonstrate that residues Leu143, Pro144 and Met145 in the gamma-turn loop play a crucial role in the binding. Further evidence is provided by the ability of vitamin D(3) to block the binding of a specific mAb in the gamma-turn loop. Using the mouse (n = 95) as an animal model, we initially demonstrated that LG is a major fraction of milk proteins responsible for uptake of vitamin D. Most interestingly, dosing mice with LG supplemented with vitamin D(3) revealed that native LG containing two binding sites gave a saturated concentration of plasma 25-hydroxyvitamin D at a dose ratio of 2 : 1 (vitamin D(3)/LG), whereas heated LG containing one exosite (lacking a central calyx) gave a ratio of 1 : 1. We have demonstrated for the first time that LG has a functional advantage in the transport of vitamin D, indicating that supplementing milk with vitamin D effectively enhances its uptake.
URI: http://dx.doi.org/10.1111/j.1742-4658.2009.06953.x
http://hdl.handle.net/11536/7421
ISSN: 1742-464X
DOI: 10.1111/j.1742-4658.2009.06953.x
期刊: FEBS JOURNAL
Volume: 276
Issue: 8
起始頁: 2251
結束頁: 2265
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