Henderson P J
Department of Biochemistry, University of Cambridge, United Kingdom.
J Bioenerg Biomembr. 1990 Aug;22(4):525-69. doi: 10.1007/BF00762961.
The cell membranes of various bacteria contain proton-linked transport systems for D-xylose, L-arabinose, D-galactose, D-glucose, L-rhamnose, L-fucose, lactose, and melibiose. The melibiose transporter of E. coli is linked to both Na+ and H+ translocation. The substrate and inhibitor specificities of the monosaccharide transporters are described. By locating, cloning, and sequencing the genes encoding the sugar/H+ transporters in E. coli, the primary sequences of the transport proteins have been deduced. Those for xylose/H+, arabinose/H+, and galactose/H+ transport are homologous to each other. Furthermore, they are just as similar to the primary sequences of the following: glucose transport proteins found in a Cyanobacterium, yeast, alga, rat, mouse, and man; proteins for transport of galactose, lactose, or maltose in species of yeast; and to a developmentally regulated protein of Leishmania for which a function is not yet established. Some of these proteins catalyze facilitated diffusion of the sugar without cation transport. From the alignments of the homologous amino acid sequences, predictions of common structural features can be made: there are likely to be twelve membrane-spanning alpha-helices, possibly in two groups of six; there is a central hydrophilic region, probably comprised largely of alpha-helix; the highly conserved amino acid residues (40-50 out of 472-522 total) form discrete patterns or motifs throughout the proteins that are presumably critical for substrate recognition and the molecular mechanism of transport. Some of these features are found also in other transport proteins for citrate, tetracycline, lactose, or melibiose, the primary sequences of which are not similar to each other or to the homologous series of transporters. The glucose/Na+ transporter of rabbit and man is different in primary sequence to all the other sugar transporters characterized, but it is homologous to the proline/Na+ transporter of E. coli, and there is evidence for its structural similarity to glucose/H+ transporters in Plants. In vivo and in vitro mutagenesis of the lactose/H+ and melibiose/Na+ (H+) transporters of E. coli has identified individual amino acid residues alterations of which affect sugar and/or cation recognition and parameters of transport. Most of the bacterial transport proteins have been identified and the lactose/H+ transporter has been purified. The directions of future investigations are discussed.
各种细菌的细胞膜含有与质子相偶联的转运系统，用于转运D-木糖、L-阿拉伯糖、D-半乳糖、D-葡萄糖、L-鼠李糖、L-岩藻糖、乳糖和蜜二糖。大肠杆菌的蜜二糖转运蛋白与Na⁺和H⁺的转运都有关联。文中描述了单糖转运蛋白的底物和抑制剂特异性。通过定位、克隆和测序大肠杆菌中编码糖/H⁺转运蛋白的基因，已推断出转运蛋白的一级序列。木糖/H⁺、阿拉伯糖/H⁺和半乳糖/H⁺转运蛋白的一级序列彼此同源。此外，它们与以下蛋白的一级序列也同样相似：在一种蓝细菌、酵母、藻类、大鼠、小鼠和人类中发现的葡萄糖转运蛋白；酵母中转运半乳糖、乳糖或麦芽糖的蛋白；以及利什曼原虫中一种功能尚未明确的发育调控蛋白。其中一些蛋白催化糖的易化扩散而不伴随阳离子转运。根据同源氨基酸序列的比对，可以预测出共同的结构特征：可能有12个跨膜α螺旋，可能分为两组，每组6个；有一个中央亲水区域，可能主要由α螺旋组成；高度保守的氨基酸残基（在总共472 - 522个氨基酸中占40 - 50个）在整个蛋白质中形成离散的模式或基序，推测这些对于底物识别和转运的分子机制至关重要。在其他转运柠檬酸、四环素、乳糖或蜜二糖的蛋白中也发现了其中一些特征，这些蛋白的一级序列彼此之间以及与同源系列的转运蛋白都不相似。兔和人的葡萄糖/Na⁺转运蛋白在一级序列上与所有其他已鉴定的糖转运蛋白不同，但它与大肠杆菌的脯氨酸/Na⁺转运蛋白同源，并且有证据表明它与植物中的葡萄糖/H⁺转运蛋白在结构上相似。对大肠杆菌的乳糖/H⁺和蜜二糖/Na⁺（H⁺）转运蛋白进行体内和体外诱变，已确定个别氨基酸残基的改变会影响糖和/或阳离子的识别以及转运参数。大多数细菌转运蛋白已被鉴定出来，乳糖/H⁺转运蛋白已被纯化。文中还讨论了未来研究的方向。
