Guntaka Naga Sandhya, Healy Alan R, Crawford Jason M, Herzon Seth B, Bruner Steven D
Department of Chemistry, University of Florida , Gainesville, Florida 32611, United States.
Department of Chemistry, Yale University , New Haven, Connecticut 06520, United States.
ACS Chem Biol. 2017 Oct 20;12(10):2598-2608. doi: 10.1021/acschembio.7b00479. Epub 2017 Sep 8.
Colibactin is a genotoxic hybrid nonribosomal peptide/polyketide secondary metabolite produced by various pathogenic and probiotic bacteria residing in the human gut. The presence of colibactin metabolites has been correlated to colorectal cancer formation in several studies. The specific function of many gene products in the colibactin gene cluster can be predicted. However, the role of ClbQ, a type II editing thioesterase, has not been established. The importance of ClbQ has been demonstrated by genetic deletions that abolish colibactin cytotoxic activity, and recent studies suggest an atypical role in releasing pathway intermediates from the assembly line. Here we report the 2.0 Å crystal structure and biochemical characterization of ClbQ. Our data reveal that ClbQ exhibits greater catalytic efficiency toward acyl-thioester substrates as compared to precolibactin intermediates and does not discriminate among carrier proteins. Cyclized pyridone-containing colibactins, which are off-pathway derivatives, are not viable substrates for ClbQ, while linear precursors are, supporting a role of ClbQ in facilitating the promiscuous off-loading of premature precolibactin metabolites and novel insights into colibactin biosynthesis.
大肠杆菌素是一种具有基因毒性的杂合非核糖体肽/聚酮类次级代谢产物，由存在于人类肠道中的多种致病和益生菌产生。在多项研究中，大肠杆菌素代谢产物的存在与结直肠癌的形成有关。大肠杆菌素基因簇中许多基因产物的具体功能可以预测。然而，II型编辑硫酯酶ClbQ的作用尚未明确。基因缺失实验证明了ClbQ的重要性，这些实验消除了大肠杆菌素的细胞毒性活性，最近的研究表明它在从装配线上释放途径中间体方面具有非典型作用。在此，我们报告了ClbQ的2.0 Å晶体结构和生化特性。我们的数据显示，与前大肠杆菌素中间体相比，ClbQ对酰基硫酯底物表现出更高的催化效率，并且对载体蛋白没有选择性。含环化吡啶酮的大肠杆菌素是偏离途径的衍生物，不是ClbQ的可行底物，而线性前体则是，这支持了ClbQ在促进过早的前大肠杆菌素代谢产物的随意卸载中的作用，并为大肠杆菌素生物合成提供了新的见解。
