Department of Chemical Engineering, Konkuk University, Seoul 143-701, Republic of Korea.
Bioorg Med Chem Lett. 2011 Oct 15;21(20):6085-9. doi: 10.1016/j.bmcl.2011.08.058. Epub 2011 Aug 19.
Type III polyketide synthases (PKSs) are the condensing enzymes that catalyze the formation of a myriad of aromatic polyketides in plant, bacteria, and fungi. Here we report the cloning and characterization of a putative type III PKS from Aspergillusniger, AnPKS. This enzyme catalyzes the synthesis of alkyl pyrones from C2 to C18 starter CoA thioesters with malonyl-CoA as an extender CoA through decaboxylative condensation and cyclization. It displays broad substrate specificity toward fatty acyl-CoA starters to yield triketide and tetraketide pyrones, with benzoyl-CoA as the most preferred starter. The optimal temperature and pH of AnPKS are 50°C and 8, respectively. Under optimal conditions, the enzyme shows the highest catalytic efficiency (k(cat)/K(m)) of 7.4×10(5)s(-1)M(-1) toward benzoyl-CoA. Homology modeling and site-directed mutagenesis were used to probe the molecular basis of its substrate specificity. This study should open doors for further engineering of AnPKS as a biocatalyst for synthesis of value-added polyketides.
III 型聚酮合酶（PKS）是缩合酶，可催化植物、细菌和真菌中众多芳香聚酮的形成。在这里，我们报道了来自黑曲霉的一个假定的 III 型 PKS（AnPKS）的克隆和表征。该酶可催化从 C2 到 C18 的起始 CoA 硫酯与丙二酰-CoA 作为扩展 CoA 的烷基吡喃酮的合成，通过去羧基缩合和环化。它对脂肪酸酰基-CoA 起始物表现出广泛的底物特异性，生成三酮和四酮吡喃酮，以苯甲酰-CoA 为最优选的起始物。AnPKS 的最佳温度和 pH 值分别为 50°C 和 8。在最佳条件下，该酶对苯甲酰-CoA 的催化效率（k(cat)/K(m)）最高，为 7.4×10(5)s(-1)M(-1)。同源建模和定点突变用于探测其底物特异性的分子基础。这项研究应该为进一步工程化 AnPKS 作为生物催化剂合成增值聚酮开辟道路。
