Abstract

Sugar transporters are essential components of carbon metabolism and have been extensively studied to control sugar uptake by yeasts and filamentous fungi used in fermentation processes. Based on published information on characterized fungal sugar porters, we show that this protein family encompasses phylogenetically distinct clades. While several clades encompass transporters that seemingly specialized on specific “sugar-related” molecules (e.g., myo-inositol, charged sugar analogs), others include mostly either mono- or di/oligosaccharide low-specificity transporters. To address the issue of substrate specificity of sugar transporters, that protein primary sequences do not fully reveal, we screened “multi-species” soil eukaryotic cDNA libraries for mannose transporters, a sugar that had never been used to select transporters. We obtained 19 environmental transporters, mostly from Basidiomycota and Ascomycota. Among them, one belonged to the unusual “Fucose H⁺ Symporter” family, which is only known in Fungi for a rhamnose transporter in Aspergillus niger. Functional analysis of the 19 transporters by expression in yeast and for two of them in Xenopus laevis oocytes for electrophysiological measurements indicated that most of them showed a preference for d-mannose over other tested d-C6 (glucose, fructose, galactose) or d-C5 (xylose) sugars. For the several glucose and fructose-negative transporters, growth of the corresponding recombinant yeast strains was prevented on mannose in the presence of one of these sugars that may act by competition for the binding site. Our results highlight the potential of environmental genomics to figure out the functional diversity of key fungal protein families and that can be explored in a context of biotechnology.

Key points

• Most fungal sugar transporters accept several sugars as substrates.

• Transporters, belonging to 2 protein families, were isolated from soil cDNA libraries.

• Environmental transporters featured novel substrate specificities.

中文翻译：

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数据挖掘和功能性环境基因组学重新评估了真菌单糖转运蛋白的系统发育和功能多样性

摘要

糖转运蛋白是碳代谢的重要组成部分，并已进行了广泛的研究，以控制发酵过程中使用的酵母和丝状真菌对糖的吸收。基于已发布的有关特征性真菌糖搬运工的信息，我们显示该蛋白家族涵盖系统发育独特的进化枝。尽管有几个进化枝涵盖了转运蛋白，这些转运蛋白似乎专门针对特定的“糖相关”分子（例如，肌-肌醇，带电荷的糖类似物），其他主要包括单糖或二糖/低聚糖低特异性转运蛋白。为了解决糖转运蛋白的底物特异性问题，蛋白质的一级序列不能完全揭示，我们筛选了“多物种”土壤真核cDNA文库中的甘露糖转运蛋白，这是一种从未用于选择转运蛋白的糖。我们获得了19种环境运输工具，其中大部分来自担子菌和子囊菌。其中一个属于不寻常的“ Fucose H ⁺ Symporter”家族，该家族仅在真菌中因黑曲霉中的鼠李糖转运蛋白而闻名。通过在酵母中表达对19个转运蛋白进行功能分析，其中两个在酵母中表达用于电生理测量的非洲爪蟾卵母细胞表明，相对于其他测试的d -C6（葡萄糖，果糖，半乳糖）或d- C5（木糖）糖，它们中的大多数显示出对d-甘露糖的偏爱。对于几种葡萄糖和果糖阴性转运蛋白，在这些糖之一可能通过竞争结合位点起作用的情况下，阻止了相应重组酵母菌株在甘露糖上的生长。我们的研究结果突出了环境基因组学解决关键真菌蛋白家族功能多样性的潜力，可以在生物技术的背景下进行探索。

关键点

•大多数真菌糖转运蛋白接受几种糖作为底物。

•从土壤cDNA文库中分离出属于2个蛋白质家族的转运蛋白。

•环境转运蛋白具有新颖的底物特异性。