虎杖苯亚甲基丙酮合酶PcPKS2的表达纯化和晶体生长

Preparation and crystallization of Polygonum cuspidatum benzalacetone synthase

摘要:

植物类型Ⅲ聚酮合酶超家族 (PKSs)，又称查尔酮合酶 (Chalcone synthase，CHS) 超家族，催化合成多种植物次生代谢产物的分子骨架。苯亚甲基丙酮合酶 (Benzalacetone synthase，BAS) 催化4-香豆酰辅酶A与丙二酰辅酶A通过一步脱羧缩合反应生成苯亚甲基丙酮，是一系列具有重要生物学活性苯丁烷类化合物及其衍生物的前体化合物。前期工作从虎杖中分离出苯亚甲基丙酮合酶BAS (PcPKS2) 和1个具有CHS和BAS活性的双功能酶 (PcPKS1)。两者与超家族其他成员序列经比较，在包括门卫氨基酸Phe215和Phe265在内的重要氨基酸序列存在一定差异。已有蛋白晶体学研究结果表明，PKSs家族不同成员的功能多样性来自于酶催化位点的非常微小的构象变化。为了能够从结构上比较PcPKS2和PcPKS1双功能酶活性差异可能产生的机制，以确定其高效BAS活性的分子机理，研究利用了大肠杆菌原核表达系统过量表达了C-端融合有His6标签的重组蛋白，经纯化得到了高纯度蛋白。经过对其晶体生长条件进行摸索和优化，得到了能用于X-射线衍射的单晶，为其结构解析、催化机理研究、了解虎杖聚酮类化合物生物合成机制和该类酶在基因工程中的应用提供了基础。

Abstract:

The chalcone synthase (CHS) superfamily of the type III polyketide synthases (PKSs) generates backbones of a variety of plant secondary metabolites. Benzalacetone synthase (BAS) catalyzes a condensation reaction of decarboxylation between the substrates of 4-coumaric coenzyme A and malonyl coenzyme A to generate benzylidene acetone, whose derivatives are series of compounds with various biological activities. A BAS gene Pcpks2 and a bifunctional CHS/BAS PcPKS1 were isolated from medicinal plant P. cuspidatum. Crystallographic and structure-based mutagenesis studies indicate that the functional diversity of the CHS-superfamily enzymes is principally derived from small modifications of the active site architecture. In order to obtain an understanding of the biosynthesis of polyketides in P. cuspidatum, which has been poorly described, as well as of its activation mechanism, PcPKS2 was overexpressed in Escherichia coli as a C-terminally poly-His-tagged fusion protein, purified to homogeneity and crystallized, which is helpful for the clarification of the catalytic mechanism of the enzyme and lays the foundation for its genetic engineering manipulation.