2gj5
Crystal structure of a secondary vitamin D3 binding site of milk beta-lactoglobulin
Structural highlights
FunctionLACB_BOVIN Primary component of whey, it binds retinol and is probably involved in the transport of that molecule. Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedBeta-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 A 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 A). The second binding site, however, is near the surface at the C-terminus (residues 136-149) containing part of an alpha-helix and a beta-strand I with 17.91 A in length, while the span of vitamin D(3) is about 12.51 A. 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). Crystal structure of a secondary vitamin D3 binding site of milk beta-lactoglobulin.,Yang MC, Guan HH, Liu MY, Lin YH, Yang JM, Chen WL, Chen CJ, Mao SJ Proteins. 2008 May 15;71(3):1197-210. PMID:18004750[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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