Mather I H, Jack L J
Department of Animal Sciences, University of Maryland, College Park 20742.
J Dairy Sci. 1993 Dec;76(12):3832-50. doi: 10.3168/jds.s0022-0302(93)77726-7.
The molecular and cellular biology of the milk protein butyrophilin is reviewed. Butyrophilin constitutes more than 40% by weight of the total protein associated with the fat globule membrane of bovine milk. Closely related proteins are abundant in the fat globule membranes of many other species. Butyrophilin is synthesized as a peptide of 526 amino acids with an amino-terminal hydrophobic signal sequence of 26 amino acids, which is cleaved before secretion in association with the fat globule membrane. Hydropathy analysis and in vitro translation of butyrophilin mRNA indicate that the protein associates with membranes in a type I orientation via a single stretch of 27 hydrophobic amino acids in the approximate middle of the sequence. Evidence that butyrophilin is incorporated into fat globule membrane as a transmembrane protein and as a cytoplasmically oriented peripheral component is discussed. The carboxy-terminal sequence of butyrophilin is significantly homologous to two other proteins: ret finger protein and the 52-kDa nuclear antigen A of Sjögren's syndrome. Expression of bovine butyrophilin mRNA correlates with the onset of milk fat secretion toward the end of pregnancy and is maintained throughout lactation. The possible function of butyrophilin in the secretion of milk lipid droplets is discussed.
本文综述了乳蛋白嗜乳脂蛋白的分子与细胞生物学。嗜乳脂蛋白占牛乳脂肪球膜相关总蛋白重量的40%以上。许多其他物种的脂肪球膜中也富含密切相关的蛋白质。嗜乳脂蛋白最初被合成为一个含有526个氨基酸的肽段，其氨基端有一段26个氨基酸的疏水信号序列，该序列在与脂肪球膜结合分泌前被切割掉。对嗜乳脂蛋白mRNA的亲水性分析和体外翻译表明，该蛋白通过序列中部一段约27个疏水氨基酸以I型方向与膜结合。文中讨论了嗜乳脂蛋白作为跨膜蛋白和胞质定向外周成分整合到脂肪球膜中的证据。嗜乳脂蛋白的羧基端序列与另外两种蛋白显著同源：ret指蛋白和干燥综合征的52 kDa核抗原A。牛嗜乳脂蛋白mRNA的表达与妊娠末期乳脂肪分泌的开始相关，并在整个泌乳期持续存在。文中还讨论了嗜乳脂蛋白在乳脂滴分泌中的可能功能。
