Abstract
Recent studies have identified phosphoglucomutase 1 (PGM1) deficiency as an inherited metabolic disorder in humans. Affected patients show multiple disease phenotypes, including dilated cardiomyopathy, exercise intolerance, and hepatopathy, reflecting the central role of the enzyme in glucose metabolism. We present here the first in vitro biochemical characterization of 13 missense mutations involved in PGM1 deficiency. The biochemical phenotypes of the PGM1 mutants cluster into two groups: those with compromised catalysis and those with possible folding defects. Relative to the recombinant wild-type enzyme, certain missense mutants show greatly decreased expression of soluble protein and/or increased aggregation. In contrast, other missense variants are well behaved in solution, but show dramatic reductions in enzyme activity, with kcat/Km often <1.5% of wild-type. Modest changes in protein conformation and flexibility are also apparent in some of the catalytically impaired variants. In the case of the G291R mutant, severely compromised activity is linked to the inability of a key active site serine to be phosphorylated, a prerequisite for catalysis. Our results complement previous in vivo studies, which suggest that both protein misfolding and catalytic impairment may play a role in PGM1 deficiency.
Highlights
Phosphoglucomutase 1 deficiency is a newly described inherited disorder in humans
The in vitro biochemical phenotypes of 13 missense mutants associated with inherited phosphoglucomutase 1 (PGM1) deficiency are reported here for the first time
Our in vitro data support the view derived from previous in vivo studies [1, 3] that folding defects and/or catalytic impairment may contribute to PGM1 deficiency, depending on the missense variant involved
Summary
Phosphoglucomutase 1 deficiency is a newly described inherited disorder in humans. Results: In vitro studies of 13 missense variants associated with disease are presented. As has been shown for a growing number of metabolic disorders (6 –9), the available in vivo data suggest that inherited PGM1 deficiency fits a “loss-of-function” phenotype that may include protein misfolding, in addition to conventional catalytic defects. Other possibilities, such as problems with protein oligomerization or cellular trafficking are unlikely, because PGM1 is a monomeric protein found in the cytosol of the cell. Proteins were characterized for expression, solubility, conformational flexibility, and stability We establish in this recombinant system that PGM1 missense variants segregate into two categories: those with severe catalytic defects and those that primarily appear to affect folding/ solubility relative to the behavior of WT enzyme. This work provides an essential baseline for future in vivo and clinical studies of PGM1 variants associated with disease
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