Functional diversity of chalcone synthase

查尔酮合成酶(CHS)超家族的III型多酮合成酶(PKS)是类黄酮生物合成的关键酶，也是一系列结构多样、具有重要生物学意义的天然产物。苯丙酮合成酶(BAS)(EC2.3.1)催化4-香豆酰辅酶A(1)与丙二酰辅酶A(1)一步脱羧基缩合生成二酮基苯丙酮。而CHS(EC 2.3.1.4-香豆酰辅酶A与丙二酰辅酶A的三个醋酸酯单元依次缩合，然后进行Claisen环化反应，形成四酮柚皮苷查尔酮。BAS被认为对大黄中的抗炎糖苷、姜辣素和生姜中的姜黄素等多种具有生物活性的苯基丁烷类化合物的C6-C4部分的构建起着至关重要的作用，它接受甲基丙二酰辅酶A作为链延伸底物，生成新的C6-C5化合物。该基因编码一个42 kDa的蛋白质，编码60-75%的氨基酸…。与CHS超家族酶的其他成员有更多的d序列同源性。紫花苜蓿CHS是一种42 kDa的同源二聚体蛋白质，最近的结晶学和蛋白质工程学研究揭示了查尔酮形成反应的活性部位机制，该反应通过Cysl164上的起始分子负载、丙二酸辅酶A脱羧基、聚酮链延长，然后酶结合的四酮中间体的环化和芳构化进行。因此，CHS的催化中心由四个氨基酸残基组成：催化三联体Cys164、His303和Asn336，以及“守门人”Phe215，除BAS外，在所有已知的III型中都是绝对保守的。在CHS中，位于活性中心空腔和CoA结合隧道之间的Phe215被认为有助于丙二酰辅酶A的脱羧基，并有助于在连续的缩合反应中定位底物和中间体。我们通过构建突变的棕榈根霉BAS，成功地证明了BAS保持了CHS活性，其中的~&lt；214&gt；IL残基被LF取代。较少

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