Gutiérrez-Adán A, Maga E A, Meade H, Shoemaker C F, Medrano J F, Anderson G B, Murray J D
University of California, Davis 95616, USA.
J Dairy Sci. 1996 May;79(5):791-9. doi: 10.3168/jds.S0022-0302(96)76427-5.
kappa-Casein is the protein fraction of milk that allows formation of micelles and determines micelle size and function, thus affecting many of the physical characteristics of milk. Several lines of transgenic mice were generated bearing the B allele of the bovine kappa-CN gene under the control of the regulatory sequences of the caprine beta-CN gene that specifically directed expression of bovine kappa-CN to the lactating mammary tissue of these mice. High expression of bovine kappa-CN protein was observed in the lines studied; the total level of protein in milk was not significantly affected. A high degree of conservation in the amino acids involved in the predicted three-dimensional structure exists between murine and bovine kappa-CN. Milk from transgenic lines expressing high bovine kappa-CN had a significantly smaller micelle size than did control milk. Therefore, bovine kappa-CN appears to have effectively participated in assembly of murine casein micelles. There was no effect on the time of rennet coagulation, but the association was significant between the milk of transgenic lines and the production of a stronger curd in rennet-induced gels. We conclude that bovine kappa-CN is an appropriate candidate for transgenic technology that would increase the ratio of kappa-CN to the calcium-sensitive caseins, therefore affecting the physical properties of the colloidal casein suspension.
κ-酪蛋白是牛奶中的蛋白质组分，它能促使胶粒形成，并决定胶粒的大小和功能，从而影响牛奶的许多物理特性。通过转基因技术培育出了几系小鼠，这些小鼠携带牛κ-酪蛋白基因的B等位基因，该基因受山羊β-酪蛋白基因调控序列的控制，可将牛κ-酪蛋白的表达特异性导向这些小鼠的泌乳乳腺组织。在所研究的品系中观察到了牛κ-酪蛋白的高表达；牛奶中的总蛋白水平未受到显著影响。小鼠和牛的κ-酪蛋白在预测的三维结构中所涉及的氨基酸具有高度保守性。表达高牛κ-酪蛋白的转基因品系的牛奶胶粒大小明显小于对照牛奶。因此，牛κ-酪蛋白似乎有效地参与了小鼠酪蛋白胶粒的组装。凝乳酶凝固时间没有受到影响，但转基因品系的牛奶与凝乳酶诱导凝胶中更强凝乳的产生之间存在显著关联。我们得出结论，牛κ-酪蛋白是转基因技术的合适候选对象，该技术可提高κ-酪蛋白与钙敏感酪蛋白的比例，从而影响胶体酪蛋白悬浮液的物理性质。
