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首页> 外文期刊>Journal of bacteriology >Sugar Transport through Maltoporin of Escherichia coli: Role of the Greasy Slide
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Sugar Transport through Maltoporin of Escherichia coli: Role of the Greasy Slide

机译：通过大肠杆菌的maltoporin的糖运输：油腻幻灯片的作用。

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The lining of the maltodextrin-specific maltoporin (LamB) channel exhibits a string of aromatic residues, the greasy slide, part of which has been shown previously by crystallography to be involved in substrate binding. To probe the functional role of the greasy slide, alanine scanning mutagenesis has been performed on the six greasy slide residues and Y118 at the channel constriction. The mutants were characterized by an in vivo uptake assay and sugar-induced-current-noise analysis. Crystallographic analysis of the W74A mutant showed no perturbation of the structure. All mutants showed considerably decreased maltose uptake rates in vivo (<10% of the wild-type value), indicating the functional importance of the investigated residues. Substitutions at the channel center revealed appreciably increased (up to 100-fold) in vitro half-saturation concentrations for maltotriose and maltohexaose binding to the channel. Sugar association rates, however, were significantly affected also by the mutations at either end of the slide (W74A, W358A, and F227A), an effect which became most apparent upon nonsymmetrical sugar addition. The kinetic data are discussed on the basis of an asymmetric one-site two-barrier model, which suggests that, at low substrate concentrations, as are found under physiological conditions, only the heights of the extracellular and periplasmic barriers, which are reduced by the presence of the greasy slide, determine the efficiency of this facilitated diffusion channel.
机译：麦芽糊精特异性麦芽糖蛋白（LamB）通道的衬里显示出一串芳香残基，油腻的载玻片，以前已通过晶体学显示其一部分与底物结合有关。为了探测油脂滑片的功能作用，已对六个油脂滑片残基和通道狭窄处的Y118进行了丙氨酸扫描诱变。通过体内摄取测定和糖诱导的电流噪声分析来表征突变体。 W74A突变体的晶体学分析显示没有扰动的结构。所有突变体均显示体内麦芽糖摄取率显着降低（<野生型值的10％），表明所研究残基的功能重要性。通道中心的取代显示出麦芽三糖和麦芽六糖结合到通道的体外半饱和浓度明显增加（最高100倍）。但是，糖结合率也受到玻片任一末端的突变（W74A，W358A和F227A）的显着影响，这种影响在添加非对称糖后最明显。在一个不对称的一部位两屏障模型的基础上讨论了动力学数据，该模型表明，在低底物浓度下（如在生理条件下发现的那样），仅胞外和周质屏障的高度会被降低。油滑玻片的存在，决定了这种促进扩散通道的效率。

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