Taheri-Kafrani Asghar, Bordbar Abdol-Khalegh, Mousavi Seyed Habib-Allah, Haertlé Thomas
Laboratory of Biophysical Chemistry, Department of Chemistry, University of Isfahan, Isfahan, 81746-73441, Islamic Republic of Iran.
J Agric Food Chem. 2008 Aug 27;56(16):7528-34. doi: 10.1021/jf801179k. Epub 2008 Aug 5.
Bovine beta-lactoglobulin (beta-LG) in vivo (in milks) has been found in complexes with lipids such as butyric and oleic acids. To elucidate the still unknown structure-function relationship in this protein, the structural changes of beta-lactoglobulin variant A (beta-LG A) in the presence of anionic surfactant such as sodium n-dodecyl sulfate (SDS) and in the presence of nonionic surfactant such as Triton X-100 have been investigated. Subsequently, the retinol binding by beta-LG has been investigated in the presence of various amounts of these surfactants as its binding indicator. The results of UV-vis and fluorescence studies show a higher denaturating effect of SDS at acid pH that can be due to greater positive charges of beta-LG at this pH indicating also the nonspecific hydrophobic interactions of Triton X-100 with beta-LG at all studied pHs. Isothermal titration calorimetry (ITC) measurements indicate the endothermic nature of beta-LG/SDS interactions and the exothermic nature of Triton X-100/beta-LG interactions. The analysis of the binding data demonstrates the absence of considerable changes in retinol binding properties of beta-LG in the presence of various amounts of these surfactants. This implies that surfactant binding does not change the conformation of beta-LG in the regions defining the retinol-binding site.
已发现牛β-乳球蛋白（β-LG）在体内（在牛奶中）与丁酸和油酸等脂质形成复合物。为阐明该蛋白质中仍未知的结构-功能关系，研究了β-乳球蛋白变体A（β-LG A）在阴离子表面活性剂如正十二烷基硫酸钠（SDS）存在下以及在非离子表面活性剂如 Triton X-100存在下的结构变化。随后，以视黄醇结合作为其结合指标，研究了在各种量的这些表面活性剂存在下β-LG与视黄醇的结合情况。紫外可见光谱和荧光研究结果表明，SDS在酸性pH下具有更高的变性作用，这可能是由于β-LG在该pH下带有更多正电荷，同时也表明在所有研究的pH下 Triton X-100与β-LG存在非特异性疏水相互作用。等温滴定量热法（ITC）测量表明β-LG/SDS相互作用具有吸热性质而 Triton X-100/β-LG相互作用具有放热性质。结合数据的分析表明，在各种量的这些表面活性剂存在下，β-LG的视黄醇结合特性没有明显变化。这意味着表面活性剂结合不会改变β-LG在定义视黄醇结合位点区域的构象。
