Pseudoenzymes have emerged as key regulatory elements in all kingdoms of life despite being catalytically nonactive. Yet many factors defining why one protein is active while its homologue is inactive remain uncertain. For pseudoenzyme–enzyme pairs, the similarity of both subunits can often hinder conventional characterization approaches. In plants, a pseudoenzyme, PDX1.2, positively regulates vitamin B₆ production by association with its active catalytic homologues such as PDX1.3 through an unknown assembly mechanism. Here we used an integrative experimental approach to learn that such pseudoenzyme–enzyme pair associations result in heterocomplexes of variable stoichiometry, which are unexpectedly tunable. We also present the atomic structure of the PDX1.2 pseudoenzyme as well as the population averaged PDX1.2–PDX1.3 pseudoenzyme–enzyme pair. Finally, we dissected hetero-dodecamers of each stoichiometry to understand the arrangement of monomers in the heterocomplexes and identified symmetry-imposed preferences in PDX1.2–PDX1.3 interactions. Our results provide a new model of pseudoenzyme–enzyme interactions and their native heterogeneity.

中文翻译：

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植物假酶-酶复合物的可调异组装

尽管没有催化活性，但假酶已成为所有生命王国中的关键调节元素。然而，定义为什么一种蛋白质具有活性而其同系物不具有活性的许多因素仍然不确定。对于假酶-酶对，两个亚基的相似性通常会阻碍传统的表征方法。在植物中，假酶 PDX1.2 可正向调节维生素 B ₆通过未知的组装机制与其活性催化同系物（如 PDX1.3）结合产生。在这里，我们使用综合实验方法来了解这种假酶-酶对关联会产生可变化学计量的异质复合物，这是出乎意料的可调谐。我们还介绍了 PDX1.2 假酶的原子结构以及群体平均 PDX1.2–PDX1.3 假酶-酶对。最后，我们剖析了每种化学计量的异十二聚体，以了解异络复合物中单体的排列，并确定了 PDX1.2–PDX1.3 相互作用中的对称性强加偏好。我们的结果提供了一种假酶-酶相互作用及其天然异质性的新模型。