Gunn F J, Tate C G, Sansom C E, Henderson P J
Department of Biochemistry, University of Cambridge, UK.
Mol Microbiol. 1995 Feb;15(4):771-83. doi: 10.1111/j.1365-2958.1995.tb02384.x.
The transport of L-fucose into Escherichia coli is mediated by the L-fucose-H+ symport protein (FucP). The fucP gene has been sequenced and encodes a hydrophobic protein that contains 438 amino acid residues, with a predicted M(r) of 47,773. The hydropathic profile of FucP indicates 10 to 12 hydrophobic regions that could span the membrane as alpha-helices. A 12-helix model with the N- and C-termini located in the cytoplasm was derived from the hydropathic profile and from application of the 'positive inside' rule. This model was tested using beta-lactamase fusion technology. Analyses of 62 different FucP-beta-lactamase fusions suggested that the FucP protein crosses the cytoplasmic membrane of E. coli 12 times, with the N- and C-termini in the cytoplasm. From measurements of [14C]-L-fucose uptake, it was deduced that the last putative transmembrane region must be complete for transport activity to be retained and that the four C-terminal residues were unnecessary for transport activity. Fourier transform analyses show that all the predicted helices contain a periodicity that enables hydrophobic/hydrophilic faces to be identified; these were particularly evident in putative helices 1, 3, 4, 5, 6, 10 and 11.
L-岩藻糖进入大肠杆菌的转运由L-岩藻糖-H⁺同向转运蛋白（FucP）介导。fucP基因已被测序，编码一个含有438个氨基酸残基的疏水蛋白，预测相对分子质量为47773。FucP的亲水性图谱表明有10至12个疏水区域，可能以α-螺旋形式跨越细胞膜。根据亲水性图谱并应用“正内则”得出一个N端和C端位于细胞质中的12螺旋模型。使用β-内酰胺酶融合技术对该模型进行了测试。对62种不同的FucP-β-内酰胺酶融合体的分析表明，FucP蛋白跨越大肠杆菌的细胞质膜12次，N端和C端位于细胞质中。通过对[¹⁴C]-L-岩藻糖摄取的测量推断，最后一个假定的跨膜区域必须完整才能保留转运活性，而C端的四个残基对于转运活性是不必要的。傅里叶变换分析表明，所有预测的螺旋都包含一种周期性，从而能够识别疏水/亲水表面；这些在假定的螺旋1、3、4、5、6、10和11中尤为明显。
