Harvey Barbara M, Hong Hui, Jones Michelle A, Hughes-Thomas Zoë A, Goss Rebecca M, Heathcote Michelle L, Bolanos-Garcia Victor M, Kroutil Wolfgang, Staunton James, Leadlay Peter F, Spencer Jonathan B
The University Chemical Laboratory, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, UK.
Chembiochem. 2006 Sep;7(9):1435-42. doi: 10.1002/cbic.200500474.
Polyether ionophores, such as monensin A, are known to be biosynthesised, like many other antibiotic polyketides, on giant modular polyketide synthases (PKSs), but the intermediates and enzymes involved in the subsequent steps of oxidative cyclisation remain undefined. In particular there has been no agreement on the mechanism and timing of the final polyketide chain release. We now report evidence that MonCII from the monensin biosynthetic gene cluster in Streptomyces cinnamonensis, which was previously thought to be an epoxide hydrolase, is a novel thioesterase that belongs to the alpha/beta-hydrolase structural family and might catalyse this step. Purified recombinant MonCII was found to hydrolyse several thioester substrates, including an N-acetylcysteamine thioester derivative of monensin A. Further, incubation with a hallmark inhibitor of such enzymes, phenylmethanesulfonyl fluoride, led to inhibition of the thioesterase activity and to the accumulation of an acylated form of MonCII. These findings require a reassessment of the role of other enzymes implicated in the late stages of polyether ionophore biosynthesis.
聚醚离子载体，如莫能菌素A，已知与许多其他抗生素聚酮化合物一样，是在巨大的模块化聚酮合酶（PKS）上生物合成的，但参与后续氧化环化步骤的中间体和酶仍不明确。特别是在最终聚酮链释放的机制和时间上尚未达成共识。我们现在报告证据表明，来自肉桂链霉菌莫能菌素生物合成基因簇的MonCII，以前被认为是一种环氧化物水解酶，是一种新型硫酯酶，属于α/β-水解酶结构家族，可能催化这一步骤。纯化的重组MonCII被发现可水解几种硫酯底物，包括莫能菌素A的N-乙酰半胱氨酸硫酯衍生物。此外，与这类酶的标志性抑制剂苯甲基磺酰氟一起孵育会导致硫酯酶活性受到抑制，并导致MonCII的酰化形式积累。这些发现需要重新评估聚醚离子载体生物合成后期其他相关酶的作用。
