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: | 1-四月-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 |
顯示於類別: | 期刊論文 |