Abstract
Colchicine is a toxic alkaloid prevalent in autumn crocus (Colchicum autumnale) that binds to tubulin and inhibits polymerization of microtubules. Using combinatorial and rational protein design, we have developed an artificial binding protein based on the human lipocalin 2 that binds colchicine with a dissociation constant of 120 pm, i.e. 10000-fold stronger than tubulin. Crystallographic analysis of the engineered lipocalin, dubbed Colchicalin, revealed major structural changes in the flexible loop region that forms the ligand pocket at the open end of the eight-stranded β-barrel, resulting in a lid-like structure over the deeply buried colchicine. A cis-peptide bond between residues Phe71 and Pro72 in loop #2 constitutes a peculiar feature and allows intimate contact with the tricyclic ligand. Using directed evolution, we achieved an extraordinary dissociation half-life of more than 9 h for the Colchicalin-colchicine complex. Together with the chemical robustness of colchicine and availability of activated derivatives, this also opens applications as a general-purpose affinity reagent, including facile quantification of colchicine in biological samples. Given that engineered lipocalins, also known as Anticalin® proteins, represent a class of clinically validated biopharmaceuticals, Colchicalin may offer a therapeutic antidote to scavenge colchicine and reverse its poisoning effect in situations of acute intoxication.
摘要 秋水仙(Colchicum autumnale)中广泛存在的一种有毒生物碱——秋水仙碱,可以结合到微管蛋白上并抑制微管聚合。通过组合和有理蛋白设计,我们开发出了一种基于人类脂联素2的人工结合蛋白,该蛋白与秋水仙碱结合的解离常数为120 pm,即比微管蛋白强10000倍。对这种工程脂联素(被称为Colchicalin)进行晶体学分析,发现在形成开放端的八股β桶的配体口袋的柔性环区域中发生了重大的结构变化,导致一个盖子状的结构覆盖在深埋的秋水仙碱上。在环#2中的Phe71和Pro72残基之间的cis-肽键构成了一种奇特的特征,并允许与三环配体进行亲密接触。通过定向进化,我们实现了Colchicalin-秋水仙碱复合物超过9小时的非解离半衰期。结合秋水仙碱的化学稳定性和活化衍生物的可用性,这也为作为通用亲和试剂(包括在生物样品中容易定量的秋水仙碱)开启了应用。鉴于工程脂联素(也称为Anticalin®蛋白)代表一类经过临床验证的生物制药,Colchicalin可能为在急性中毒情况下清除秋水仙碱并逆转其中毒作用提供治疗解药。