More than half of disease-causing missense variants are thought to lead to protein degradation, but the molecular mechanism of how these variants are recognized by the cell remains enigmatic. Degrons are stretches of amino acids that help mediate recognition by E3 ligases and thus confer protein degradation via the ubiquitin-proteasome system. While degrons that mediate controlled degradation of, for example, signaling components and cell-cycle regulators are well described, so-called protein-quality-control degrons that mediate the degradation of destabilized proteins are poorly understood. Here, we show that disease-linked dihydrofolate reductase (DHFR) missense variants are structurally destabilized and chaperone-dependent proteasome targets. We find two regions in DHFR that act as degrons, and the proteasomal turnover of one of these was dependent on the molecular chaperone Hsp70. Structural analyses by nuclear magnetic resonance (NMR) and hydrogen/deuterium exchange revealed that this degron is buried in wild-type DHFR but becomes transiently exposed in the disease-linked missense variants.

超过一半的致病错义变异被认为会导致蛋白质降解，但这些变异如何被细胞识别的分子机制仍然是个谜。Degrons 是一段氨基酸，有助于介导 E3 连接酶的识别，从而通过泛素-蛋白酶体系统进行蛋白质降解。虽然介导例如信号成分和细胞周期调节剂的受控降解的 degrons 得到了很好的描述，但对介导不稳定蛋白质降解的所谓蛋白质质量控​​制 degrons 知之甚少。在这里，我们表明与疾病相关的二氢叶酸还原酶 (DHFR) 错义变体在结构上不稳定且依赖伴侣蛋白的蛋白酶体靶标。我们在 DHFR 中发现两个区域作为 degrons，其中一种的蛋白酶体更新依赖于分子伴侣 Hsp70。通过核磁共振 (NMR) 和氢/氘交换进行的结构分析表明，这种 degron 隐藏在野生型 DHFR 中，但在与疾病相关的错义变体中暂时暴露。