ABCG2 is an important ATP-binding cassette transporter impacting the absorption and distribution of over 200 chemical toxins and drugs. ABCG2 also reduces the cellular accumulation of diverse chemotherapeutic agents. Acquired somatic mutations in the phylogenetically conserved amino acids of ABCG2 might provide unique insights into its molecular mechanisms of transport. Here, we identify a tumor-derived somatic mutation (Q393K) that occurs in a highly conserved amino acid across mammalian species. This ABCG2 mutant seems incapable of providing ABCG2-mediated drug resistance. This was perplexing because it is localized properly and retained interaction with substrates and nucleotides. Using a conformationally sensitive antibody, we show that this mutant appears “locked” in a non-functional conformation. Structural modeling and molecular dynamics simulations based on ABCG2 cryo-EM structures suggested that the Q393K interacts with the E446 to create a strong salt bridge. The salt bridge is proposed to stabilize the inward-facing conformation, resulting in an impaired transporter that lacks the flexibility to readily change conformation, thereby disrupting the necessary communication between substrate binding and transport.

中文翻译：

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肿瘤获得性体细胞突变影响构象以消除 ABCG2 介导的耐药性

ABCG2 是一种重要的 ATP 结合盒转运蛋白，影响 200 多种化学毒素和药物的吸收和分布。ABCG2 还可以减少多种化疗药物的细胞积累。ABCG2 系统发育保守氨基酸的获得性体细胞突变可能为其分子运输机制提供独特的见解。在这里，我们鉴定了一种肿瘤源性体细胞突变（Q393K），该突变发生在哺乳动物物种中高度保守的氨基酸中。这种 ABCG2 突变体似乎无法提供 ABCG2 介导的耐药性。这是令人困惑的，因为它被正确定位并保留了与底物和核苷酸的相互作用。使用构象敏感的抗体，我们发现该突变体似乎“锁定”在非功能性构象中。基于 ABCG2 冷冻电镜结构的结构建模和分子动力学模拟表明，Q393K 与 E446 相互作用，形成强盐桥。盐桥被认为是为了稳定向内的构象，导致转运蛋白受损，缺乏容易改变构象的灵活性，从而破坏底物结合和运输之间必要的通讯。