Department of Plant and Environmental Sciences and Copenhagen Plant Science Center, University of Copenhagen, Denmark.
Department of Food Science, University of Copenhagen, Denmark.
Plant Physiol. 2022 Mar 4;188(3):1483-1495. doi: 10.1093/plphys/kiab545.
In the wild cruciferous wintercress (Barbarea vulgaris), β-amyrin-derived saponins are involved in resistance against insect herbivores like the major agricultural pest diamondback moth (Plutella xylostella). Enzymes belonging to the 2,3-oxidosqualene cyclase family have been identified and characterized in B. vulgaris G-type and P-type plants that differ in their natural habitat, insect resistance and saponin content. Both G-type and P-type plants possess highly similar 2,3-oxidosqualene cyclase enzymes that mainly produce β-amyrin (Barbarea vulgaris Lupeol synthase 5 G-Type; BvLUP5-G) or α-amyrin (Barbarea vulgaris Lupeol synthase 5 P-Type; BvLUP5-P), respectively. Despite the difference in product formation, the two BvLUP5 enzymes are 98% identical at the amino acid level. This provides a unique opportunity to investigate determinants of product formation, using the B. vulgaris 2,3-oxidosqualene cyclase enzymes as a model for studying amino acid residues that determine differences in product formation. In this study, we identified two amino acid residues at position 121 and 735 that are responsible for the dominant changes in generated product ratios of β-amyrin and α-amyrin in both BvLUP5 enzymes. These amino acid residues have not previously been highlighted as directly involved in 2,3-oxidosqualene cyclase product specificity. Our results highlight the functional diversity and promiscuity of 2,3-oxidosqualene cyclase enzymes. These enzymes serve as important mediators of metabolic plasticity throughout plant evolution.
在野生十字花科冬油菜（Barbarea vulgaris）中，β-香树脂烷衍生的皂苷参与了对昆虫食草动物的抗性，如农业上的主要害虫小菜蛾（Plutella xylostella）。属于 2,3-氧化鲨烯环化酶家族的酶已在 B. vulgaris G 型和 P 型植物中被鉴定和表征，这两种植物在其自然栖息地、抗虫性和皂苷含量上存在差异。G 型和 P 型植物都拥有高度相似的 2,3-氧化鲨烯环化酶，主要产生 β-香树脂醇（Barbarea vulgaris Lupeol synthase 5 G-Type；BvLUP5-G）或 α-香树脂醇（Barbarea vulgaris Lupeol synthase 5 P-Type；BvLUP5-P）。尽管产物形成存在差异，但这两种 BvLUP5 酶在氨基酸水平上有 98%的同源性。这为研究产物形成的决定因素提供了一个独特的机会，利用 B. vulgaris 2,3-氧化鲨烯环化酶作为研究决定产物形成差异的氨基酸残基的模型。在这项研究中，我们确定了位于位置 121 和 735 的两个氨基酸残基，它们负责两种 BvLUP5 酶中β-香树脂醇和 α-香树脂醇生成产物比例的主要变化。这些氨基酸残基以前没有被强调为直接参与 2,3-氧化鲨烯环化酶产物特异性。我们的结果突出了 2,3-氧化鲨烯环化酶的功能多样性和混杂性。这些酶是植物进化过程中代谢可塑性的重要介质。
