標題: Crystal structure of a secondary vitamin D(3) binding site of milk beta-lactoglobulin
作者: Yang, Ming-Chi
Guan, Hong-Hsiang
Liu, Ming-Yih
Lin, Yih-Hung
Yang, Jinn-Moon
Chen, Wen-Liang
Chen, Chun-Jung
Mao, Simon J. T.
生醫工程研究所
Institute of Biomedical Engineering
關鍵字: fluorescence ligand binding assay;crystallography;localized alternative vitamin D binding site;thermal denaturation;amphipathic helix
公開日期: 15-May-2008
摘要: beta-lactoglobulin (beta-LG), one of the most investigated proteins, is a major bovine milk protein with a predominantly beta structure. The structural function of the only alpha-helix with three turns at the C-terminus is unknown. Vitamin D(3) binds to the central calyx formed by the beta-strands. Whether there are two vitamin D binding-sites in each beta-LG molecule has been a subject of controversy. Here, we report a second vitamin D(3) binding site identified by synchrotron X-ray diffraction (at 2.4 angstrom resolution). In the central calyx binding mode, the aliphatic tail of vitamin D(3) clearly inserts into the binding cavity, where the 3-OH group of vitamin D(3) binds externally. The electron density map suggests that the 3-OH group interacts with the carbonyl of Lys-60 forming a hydrogen bond (2.97 angstrom). The second binding site, however, is near the surface at the C-terminus (residues 136-149) containing part of an a-helix and a beta-strand I with 17.91 angstrom in length, while the span of vitamin D(3) is about 12.51 angstrom. A remarkable feature of the second exosite is that it combines an amphipathic alpha-helix providing nonpolar residues (Phe-136, Ala-139, and Leu-140) and a beta-strand providing a nonpolar (Ile-147) and a buried polar residue (Arg-148). They are linked by a hydrophobic loop (Ala-142, Leu-143, Pro-144, and Met-145). Thus, the binding pocket furnishes strong hydrophobic force to stabilize vitamin D(3) binding. This finding provides a new insight into the interaction between vitamin D(3) and beta-LG, in which the exosite may provide another route for the transport of vitamin D(3) in vitamin D(3) fortified dairy products. Atomic coordinates for the crystal structure Of beta-LG-vitamin D(3) complex described in this work have been deposited in the PDB (access code 2GJ5).
URI: http://dx.doi.org/10.1002/prot.21811
http://hdl.handle.net/11536/9326
ISSN: 0887-3585
DOI: 10.1002/prot.21811
期刊: PROTEINS-STRUCTURE FUNCTION AND BIOINFORMATICS
Volume: 71
Issue: 3
起始頁: 1197
結束頁: 1210
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