題名: Rational Design for Crystallization of β-Lactoglobulin and Vitamin D3 Complex: Revealing a Secondary Binding Site
作者: Yang MC;Guan HH;Yang JM;Ko CN;Liu MY;Lin YH;Huang YC;Chen CJ;Mao SJT 貢獻者: Department of Biotechnology
日期: 2008-12
上傳時間: 2009-11-26T01:43:06Z 出版者: Asia University
摘要: β-Lactoglobulin (LG) is a major milk whey protein containing primarily a calyx for vitamin D3 binding, although the existence of another site beyond the calyx is controversial. Using
fluorescence spectral analyses in the previous study, we showed the binding stoichiometry for vitamin D3 to LG to be 2:1 and a stoichiometry of 1:1 when the calyx was “disrupted” by manipulating the pH and temperature, suggesting that a secondary vitamin D binding site existed. To help localize this secondary site using X-ray crystallography in the present study, we used bioinformatic programs (Insight II, Q-SiteFinder, and GEMDOCK) to identify the potential location of this site. We then optimized the occupancy and enhanced the electron density of vitamin D3 in the complex by altering the pH and initial ratios of vitamin D3/LG in the cocrystal preparation. We conclude that GEMDOCK can aid in searching for an extra density map around potential vitamin D binding sites. Both pH (8) and initial ratio of vitamin D3/LG (3:1) are crucial to optimize the occupancy and enhance the electron density of vitamin D3 in the complex for rational-designed crystallization. The strategy in practice may be useful for future identification of a ligand-binding site in a given protein.
