Johnson K D, Höfte H, Chrispeels M J
Department of Biology, University of California, San Diego, La Jolla 92093-0116.
Plant Cell. 1990 Jun;2(6):525-32. doi: 10.1105/tpc.2.6.525.
The tonoplast mediates the transport of various ions and metabolites between the vacuole and cytosol by mechanisms that remain to be elucidated at the molecular level. The primary structure of only one tonoplast protein, the H(+)-ATPase, has been reported to date. Here we report the primary structure of tonoplast intrinsic protein (TIP), a 27-kilodalton intrinsic membrane protein that occurs widely in the tonoplasts of the protein storage vacuoles (protein bodies) of seeds [Johnson, K.D., et al. (1989). Plant Physiol. 91, 1006-1013]. Hydropathy plots and secondary structure analysis of the polypeptide predict six membrane-spanning domains connected by short loops and hydrophilic, cytoplasmically oriented N- and C-terminal regions. TIP displays significant homology with several other membrane proteins from diverse sources: major intrinsic polypeptide from bovine lens fiber plasma membrane; NOD 26, a peribacteroid membrane protein in the nitrogen-fixing root nodules of soybean; and interestingly, GIpF, the glycerol facilitator transport protein in the cytoplasmic membrane of Escherichia coli. Based on the homology between TIP and GIpF and the knowledge that the protein storage vacuolar membrane and the peribacteroid membrane are active in solute transport, we propose that TIP transports small metabolites between the storage vacuoles and cytoplasm of seed storage tissues.
液泡膜通过一些在分子水平上仍有待阐明的机制介导各种离子和代谢物在液泡和细胞质之间的运输。迄今为止，仅报道了一种液泡膜蛋白即H(+)-ATPase的一级结构。在此，我们报道了液泡膜内在蛋白（TIP）的一级结构，它是一种27千道尔顿的内在膜蛋白，广泛存在于种子蛋白贮藏液泡（蛋白体）的液泡膜中[约翰逊，K.D.等人（1989年）。植物生理学。91，1006 - 1013]。对该多肽的亲水性图谱和二级结构分析预测有六个跨膜结构域，由短环以及亲水性的、面向细胞质的N端和C端区域相连。TIP与来自不同来源的其他几种膜蛋白具有显著的同源性：牛晶状体纤维质膜中的主要内在多肽；大豆固氮根瘤中类菌体周膜蛋白NOD 26；有趣的是，还有大肠杆菌细胞质膜中的甘油转运促进蛋白GIpF。基于TIP与GIpF之间的同源性以及蛋白贮藏液泡膜和类菌体周膜在溶质运输中具有活性这一认识，我们提出TIP在种子贮藏组织的贮藏液泡和细胞质之间运输小分子代谢物。
