Dynamic Filament Assembly Regulates the Prolyl Aminopeptidase Activity of Plant Immune Protein DM3
The alpha/beta hydrolase DANGEROUS MIX 3 (DM3), a proline aminopeptidase in Arabidopsis thaliana, contributes to stress resilience through both metabolic regulation and immune signaling. Its functions are partitioned within its oligomeric structure as a trimer-of-dimers, in which the immune regulatory switch resides at the dimer interface. While the enzymatic activity of DM3 is not necessary for…
Proline aminopeptidase DM3, a component of alpha/beta hydrolase DANGEROUS MIX 3 (DM3), plays a role in stress resilience in Arabidopsis thaliana. Its activity is essential for salt and drought tolerance, but not for immune response. The molecular mechanism behind this regulation has been a mystery. Researchers have now discovered that DM3 undergoes dynamic and reversible assembly into higher-order filaments, a process that is sensitive to salt levels.
Cryo-electron microscopy (EM) revealed that this filament formation occurs due to rearrangements of a planar hexamer into a tilted hexameric configuration. Crucially, within these filaments, one of the catalytic residues is misaligned, disrupting the enzyme's geometry and rendering it inactive. This study establishes that filament assembly serves as a mechanism to keep DM3 inactive, suggesting that the shift between different oligomeric states enables DM3 to coordinate its roles in both biotic and abiotic stress responses.
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