Functional diversity of chalcone synthase

查耳酮合酶（CHS）超家族的III型聚酮化合物合成酶（PKS）是类黄酮以及广泛的结构多样的、生物学上重要的天然产物的生物合成中的关键酶。苄叉丙酮合酶（BAS）（EC 2.3.1）催化4-香豆酰-CoA（1）与丙二酰-CoA的一步脱羧缩合以产生二酮化合物苄叉丙酮。而CHS（EC 2.3.1. 74)进行4-香豆酰-CoA与来自丙二酰-CoA的三个乙酸酯单元的顺序缩合，随后进行Claisen型环化反应，导致形成四酮化合物柚皮素查耳酮。BAS被认为在构建各种生物活性的戊基丁烷类化合物的C6-C4部分中起关键作用，包括大黄中的抗炎葡糖苷lindleyin [6]-姜辣素和姜植物中的姜黄素，BAS接受甲基-丙二酰CoA作为Achain延长底物以产生新的C6-C5化合物。该cDNA编码的蛋白质分子量为42 kDa，氨基酸含量为60-75%， ...更多信息 d与CHS-超家族酶的其他成员的序列同一性。最近的晶体学和蛋白质工程研究苜蓿（紫花苜蓿）CHS，同源二聚体42 kDa的蛋白质，揭示了查耳酮形成反应的活性位点机械，通过在Cysl 164，丙二酰辅酶A脱羧，聚酮链延伸，然后通过环化和芳构化的酶结合的四酮中间体的起始分子加载进行。因此，CHS的催化中心由四个氨基酸残基组成;催化三联体Cys 164、His 303和Asn 336，以及“守门人”Phe 215，在除BAS之外的所有已知III型中绝对保守。在CHS中，Phe 215位于活性位点空腔和CoA结合通道之间的连接处，已被提出促进丙二酰-CoA的脱羧，并在连续缩合反应期间帮助定向底物和中间体。通过构建突变体R. palmatum BAS，其中残基^<214>IL被LF取代。少

The chalcone synthase (CHS) superfamily of type III poyketide synthases (PKSs) are pivotal enzymes in the biosynthesis of flavonoids as well as a wide range of structurally diverse, biologically important natural products. Benzalacetone synthase (BAS) (EC2.3.1) catalyzes a one-step decarboxylative condensation of 4-coumaroyl-CoA (1) with malonyl-CoA to produce a diketide benzalacetone. While CHS (EC 2.3.1. 74) performs sequential condensations of 4-coumaroyl-CoA with three acetate units from malonyl-CoA followed by Claisen-type cyclization reaction, leading to formation of a tetraketide naringenin chalcone. BAS, which is thought to play a crucial role for construction of the C6-C4 moiety of a variety of biologically active penylbutanoids including anti-inflammatory glucoside lindleyin in rhubarb [6]-gingerol and curcumin in ginger plants accepted methyl-malonylCoA as achain elongation substrate to produce novel C6-C5 compounds. The cDNA encoded a 42kDa protein sharning 60-75% amino aci … More d sequence identity with other members of the CHS-superfamily enzymes. Recent crystallographic and protein engineering studies on alfalfa (Medicago sativa) CHS, a homodimeric 42 kDa protein, revealed the active site machinery of the chalcone forming reaction which proceeds through starter molecule loading at Cysl164, malony-CoA deearboxylation, polyketide chain elongation, followed by cyclization and aromatization of the enzyme bound tetraketide intermediate. The catalytic center of CHS is thus composed of four amino acid residues; the catalytic triad of Cys164, His303, and Asn336, and the "gatekeeper" Phe215, absolutely conserved in all the known type III expect as of BAS. In CHS, Phe215, located at the junction between the active site cavity and the CoA binding tunnel, has been proposed to facilitate decarboxylation of malonyl-CoA and help orient substrates and intermediates during the sequential condensation reactions. We successfully showed that BAS retained CHS activity by constructing the mutant R. palmatum BAS in which the residues ^<214>IL were substituted by LF. Less