Tunable Heteroassembly of a Plant Pseudoenzyme-Enzyme Complex

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 pseudoen-zyme-enzyme pairs, the similarity of both subunits can often hinder conventional characterization approaches. In plants, a pseudoenzyme, PDX1.2, positively regulates vitamin B-6 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 pseudoen-zyme-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.

Automated summary

Pseudoenzymes play key regulatory roles in various kingdoms of life despite their lack of catalytic activity. Research on pseudoenzyme-enzyme pairs has revealed that the similarity between the two subunits can often complicate conventional characterization approaches. Studies have shown that associations between pseudoenzyme-enzyme pairs result in heterocomplexes of variable stoichiometry, providing insight into a new model of pseudoenzyme-enzyme interactions and their native heterogeneity.