ATP-binding cassette (ABC) transporters are the largest family of ATP-hydrolyzing transporters, which import or export substrates across membranes, and have members in every sequenced genome. Structural studies and biochemistry highlight the contrast between the global structural similarity of homologous transporters and the enormous diversity of their substrates. How do ABC transporters evolve to carry such diverse molecules and what variations in their amino acid sequence alter their substrate selectivity? We mutagenized the transmembrane domains of a conserved fungal ABC transporter that exports a mating pheromone and selected for mutants that export a non-cognate pheromone. Mutations that alter export selectivity cover a region that is larger than expected for a localized substrate-binding site. Individual selected clones have multiple mutations, which have broadly additive contributions to specific transport activity. Our results suggest that multiple positions influence substrate selectivity, leading to alternative evolutionary paths toward selectivity for particular substrates and explaining the number and diversity of ABC transporters.

中文翻译：

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选择改变的底物特异性揭示了 ATP 结合盒式转运蛋白的进化灵活性。

ATP 结合盒 (ABC) 转运蛋白是最大的 ATP 水解转运蛋白家族，可跨膜导入或导出底物，并且在每个测序的基因组中都有成员。结构研究和生物化学突出了同源转运蛋白的整体结构相似性与其底物的巨大多样性之间的对比。ABC 转运蛋白如何进化以携带如此多样的分子，它们的氨基酸序列的哪些变化会改变它们的底物选择性？我们对输出交配信息素的保守真菌 ABC 转运蛋白的跨膜结构域进行了诱变，并选择了输出非同源信息素的突变体。改变输出选择性的突变覆盖的区域大于局部底物结合位点的预期区域。个别选定的克隆具有多个突变，这些突变对特定的运输活动具有广泛的累加贡献。我们的结果表明，多个位置影响底物选择性，导致对特定底物选择性的替代进化路径，并解释了 ABC 转运蛋白的数量和多样性。