Functional analysis of PRPS1 disease alleles reveals altered polymerization and cytoskeletal organization

Phosphoribosyl pyrophosphate synthetase 1 catalyzes a central step in nucleotide biosynthesis, and pathogenic variants cause a spectrum of neurological disorders ranging from loss-of-function syndromes to enzyme superactivity. Despite their opposing biochemical effects, these variants often produce overlapping phenotypes, suggesting that shared cellular processes may contribute to disease pathogenesis. Here, using Saccharomyces cerevisiae and patient-derived human fibroblasts, we examined how disease-associated variants affect phosphoribosyl pyrophosphate synthetase 1 polymerization and whether changes in assembly are associated with metabolic state and cytoskeletal organization. Human phosphoribosyl pyrophosphate synthetase 1 functionally substituted for essential phosphoribosyl pyrophosphate synthetase paralogs in Saccharomyces cerevisiae, and disease-associated variants differentially altered filament abundance, length, and architecture in ways not fully explained by changes in protein levels. Polymer assembly was sensitive to cellular metabolic state: deletion of the yeast adenosine kinase gene, a condition previously shown to elevate intracellular adenosine and S-adenosylmethionine, strongly suppressed filament formation, including in hyperpolymerizing superactivity variants. Both gain- and loss-of-function variants were associated with altered actin organization in Saccharomyces cerevisiae and patient-derived human fibroblasts, whereas the D183H superactivity variant promoted aberrant cytoplasmic polymerization in human cells. Together, these findings identify phosphoribosyl pyrophosphate synthetase 1 polymerization as a metabolically responsive feature associated with cytoskeletal organization and provide a cellular framework for understanding how functionally distinct disease alleles can converge on overlapping phenotypes.