Recent work has found that many metabolic enzymes have the ability to polymerize in response to metabolic changes or environmental stress. This ability to polymerize is well conserved for the few metabolic enzyme paralogs that have been studied in yeast. Here we describe the first set of paralogs, Asn1p and Asn2p, that have differential assembly behavior. Asn1p and Asn2p both co-assemble into filaments in response to nutrient limitation. However, the ability of Asn2p to form filaments is strictly dependent on the presence of Asn1p. Using mutations that block enzyme activity but have differential effects on Asn1p polymerization, we have found that Asn1p polymers are unlikely to have acquired a moonlighting function. Together these results provide a novel system for understanding the regulation and evolution of metabolic enzyme polymerization.

Previously, we identified yeast strains, namely SWORD, showing more robust Ald4p-GFP filament formation than the typical ALD4::GFP strains. Here, we report that Ald4p-GFP in SWORD strains favorably polymerize into gigantic structures in the cytoplasm, despite the enzyme being established as a mitochondrial resident. In addition, we have found that nocodazole, a microtubule destabilizer, has no effect on Ald4p high-order assembly, suggesting no direct association between microtubule dynamics and Ald4p structure formation. Ald4p assembly cannot be induced by sodium azide treatment, indicating that ATP is not a primary effector of Ald4p polymerization. Interestingly, addition of exogenous acetaldehyde, a substrate of the enzyme, can significantly enhance the structure formation of Ald4p, implying that structure formation may be related to enzymatic activity.