First Faculty of Medicine, Charles University in Prague and General University Hospital in Prague, Institute of Inherited Metabolic Disorders, Prague, Czech Republic.
Hum Mutat. 2010 Jul;31(7):809-19. doi: 10.1002/humu.21273.
Misfolding of mutant enzymes may play an important role in the pathogenesis of cystathionine beta-synthase (CBS) deficiency. We examined properties of a series of 27 mutant variants, which together represent 70% of known alleles observed in patients with homocystinuria due to CBS deficiency. The median amount of SDS-soluble mutant CBS polypeptides in the pellet after centrifugation of bacterial extracts was increased by 50% compared to the wild type. Moreover, mutants formed on average only 12% of tetramers and their median activity reached only 3% of the wild-type enzyme. In contrast to the wild-type CBS about half of mutants were not activated by S-adenosylmethionine. Expression at 18 degrees C substantially increased the activity of five mutants in parallel with increasing the amounts of tetramers. We further analyzed the role of solvent accessibility of mutants as a determinant of their folding and activity. Buried mutations formed on average less tetramers and exhibited 23 times lower activity than the solvent exposed mutations. In summary, our results show that topology of mutations predicts in part the behavior of mutant CBS, and that misfolding may be an important and frequent pathogenic mechanism in CBS deficiency.
突变酶的错误折叠可能在胱硫醚β-合酶（CBS）缺乏症的发病机制中起重要作用。我们研究了一系列 27 种突变变体的特性，这些变体共同代表了由于 CBS 缺乏导致同型胱氨酸尿症患者中观察到的已知等位基因的 70％。与野生型相比，细菌提取物离心后沉淀中 SDS 可溶性突变 CBS 多肽的中位数增加了 50％。此外，突变体平均仅形成 12％的四聚体，其中位数活性仅为野生型酶的 3％。与野生型 CBS 不同，大约一半的突变体不能被 S-腺苷甲硫氨酸激活。在 18°C 下表达时，与四聚体数量的增加平行，五种突变体的活性大大提高。我们进一步分析了突变体溶剂可及性作为其折叠和活性决定因素的作用。平均而言，埋藏突变形成的四聚体较少，活性比溶剂暴露突变低 23 倍。总之，我们的结果表明，突变的拓扑结构部分预测了突变 CBS 的行为，并且错误折叠可能是 CBS 缺乏症的重要和常见的发病机制。
