Iametti B S, Tedeschi G, Oungre E, Bonomi F
Dipartimento di Scienze Molecolari Agroalimentari, Università degli Studi di Milano, Italy.
J Dairy Res. 2001 Feb;68(1):53-61. doi: 10.1017/s0022029900004544.
In this work the purification and the complete primary structure of kappa-casein from equine milk are reported for the first time. Mares' milk casein was separated by RP-HPLC into four fractions. Complete primary sequence was obtained by sequence analysis of the protein in the fastest eluting peak isolated by chromatography. This sequence was 95% identical to that reported for the C-terminal portion of the zebras' kappa-casein and showed high similarity with kappa-caseins from sources other than Equidae, confirming that this protein was indeed kappa-casein in equine milk. The presence of post-translational modifications in equine kappa-casein was investigated by mass spectroscopy, after enzymic dephosphorylation. Two main components were found, the smaller component being more abundant. Equine kappa-casein was recognized by a lectin specific for one of the glucosidic bonds in the saccharide moiety of bovine kappa-casein. Sequence comparison with prevision studies showed that the distribution of charged and hydrophobic regions in equine kappa-casein was similar, but not identical, to that found in the bovine protein; these regions are associated with the role of kappa-casein in the formation and stabilization of the micellar structure of casein in milk.
本文首次报道了马奶中κ-酪蛋白的纯化及完整一级结构。马奶酪蛋白通过反相高效液相色谱法（RP-HPLC）分离为四个组分。通过对色谱分离出的洗脱最快峰中的蛋白质进行序列分析，获得了完整的一级序列。该序列与斑马κ-酪蛋白C端部分报道的序列有95%的同一性，并且与马科动物以外来源的κ-酪蛋白具有高度相似性，证实该蛋白确实是马奶中的κ-酪蛋白。在酶促去磷酸化后，通过质谱法研究了马κ-酪蛋白中翻译后修饰的存在情况。发现了两个主要成分，较小的成分更为丰富。马κ-酪蛋白被一种对牛κ-酪蛋白糖部分中的一种糖苷键具有特异性的凝集素识别。与先前研究的序列比较表明，马κ-酪蛋白中带电和疏水区域的分布与牛蛋白中的分布相似，但不完全相同；这些区域与κ-酪蛋白在牛奶中酪蛋白胶束结构形成和稳定中的作用相关。
