Department of Chemistry, University of Manitoba, Winnipeg, R3T 2N2, Canada.
Department of Microbiology, University of Manitoba, Winnipeg, R3T 2N2, Canada.
Biochem Biophys Res Commun. 2018 Sep 10;503(3):1228-1234. doi: 10.1016/j.bbrc.2018.07.029. Epub 2018 Jul 11.
Efforts by lichenologists to characterize lichen polyketide synthases (PKS) through heterologous expression experiments have so far proved unfruitful. A determination of systematic causes of failure is therefore required. Three hypotheses involving the ketosynthase (KS) domain of lichen polyketide synthases (PKS) from Cladonia uncialis are tested: (1) Horizontal versus vertical gene transfer; (2) Typical versus atypical active site residues; (3) Typical versus atypical tertiary protein structure and active site architecture. Phylogenetics, amino acid sequence alignment, and protein modelling indicate that C. uncialis PKS evolved through vertical transfer from Ascomycota fungi, possess Cys-His-His catalytic triads typical of KS from most organisms, and possess protein and catalytic site architecture identical to well-characterized KS from non-lichen organisms. Though the reason for lack of functional activity in heterologous hosts remains unknown, complications involving the KS are ruled out as a likely explanation. Heterologous translation of lichen PKS (or parts thereof) have not been reported. We demonstrate heterologous translation of two lichen KS domains in E. coli.
通过异源表达实验来描述地衣聚酮合酶（PKS）的地衣学家们迄今为止的努力都没有成功。因此，需要确定失败的系统原因。对来自 Cladonia uncialis 的地衣聚酮合酶（PKS）的酮合酶（KS）结构域进行了三个假说的检验：（1）水平转移与垂直转移；（2）典型与非典型活性位点残基；（3）典型与非典型三级蛋白结构和活性位点结构。系统发生学、氨基酸序列比对和蛋白质建模表明，C. uncialis PKS 是通过垂直基因转移从子囊菌真菌进化而来的，具有大多数生物体中 KS 所具有的 Cys-His-His 催化三联体，并且具有与非地衣生物体中经过充分表征的 KS 相同的蛋白质和催化位点结构。虽然在异源宿主中缺乏功能活性的原因尚不清楚，但 KS 涉及的复杂性被排除为可能的解释。尚未有报道称地衣 PKS（或其部分）在异源系统中进行翻译。我们证明了两个地衣 KS 结构域在大肠杆菌中的异源翻译。
