Characterization of Novel Pathogenic Variants Causing Pyridox(am)ine 5'-Phosphate Oxidase-Dependent Epilepsy

Area of Science:

• Biochemistry
• Enzymology
• Medical Genetics

Background:

• Pyridox(am)ine 5'-phosphate oxidase (PNPO) deficiency (PNPOD) is a rare genetic disorder causing neonatal epileptic encephalopathy.
• Understanding how PNPO variants affect enzyme function is crucial for elucidating disease mechanisms and developing treatments.

Purpose of the Study:

• To characterize the catalytic, allosteric, and structural properties of four recombinant PNPO variants (D33V, R161C, P213S, E50K).
• To assess the impact of these variants on enzyme function and their potential pathogenicity in PNPOD.

Main Methods:

• Recombinant expression of PNPO variants.
• Biochemical assays to determine catalytic activity and cofactor binding.
• Analysis of allosteric regulation and thermal stability.

Main Results:

• D33V and E50K variants exhibited only mild alterations in catalytic properties; E50K may be non-pathogenic.
• P213S variant showed reduced thermal stability and FMN cofactor binding.
• R161C variant significantly decreased substrate affinity and abolished product feedback inhibition.

Conclusions:

• The characterized PNPO variants display diverse functional impairments, ranging from mild to severe.
• The R161C variant's loss of substrate affinity and allosteric regulation provides insights into PNPOD pathogenesis.
• These findings contribute to understanding genotype-phenotype correlations in PNPO deficiency and inform potential therapeutic strategies.