Genetic, structural, and functional analysis of pathogenic variations causing methylmalonyl-CoA epimerase deficiency

Area of Science:

• Biochemistry
• Genetics
• Molecular Biology

Background:

• Human methylmalonyl-CoA epimerase (MCEE) is crucial for propionate metabolism.
• Pathogenic variations in MCEE cause autosomal recessive methylmalonic aciduria (MMAuria).
• Previous studies identified MMAuria in eleven patients with MCEE variations.

Purpose of the Study:

• To investigate a cohort of 150 individuals with unexplained MMAuria.
• To identify new patients with MCEE deficiency and understand the molecular basis of MCEE dysfunction.
• To elucidate the structural and functional consequences of MCEE variations.

Main Methods:

• Genetic analysis of 150 MMAuria patients to identify MCEE variations.
• Protein structure determination of wild-type (wt) and variant MCEE.
• Functional assays including protein expression, solubility, unfolding, and enzymatic activity measurements.
• Analysis of patient-derived fibroblasts.

Main Results:

• Ten new patients with MCEE deficiency were identified, including nine with p.Arg47* and one with novel p.Ile53Arg.
• Structural analysis revealed potential dimeric assembly disruption by p.Ile53Arg and significant loop structure disruption in MCEE-Arg143Cys.
• MCEE-Ile53Arg exhibited misfolding, low soluble protein levels, and lack of enzymatic activity.
• MCEE-Arg143Cys showed reduced activity and altered unfolding kinetics, while MCEE-Lys60Gln's disease mechanism remained unclear.

Conclusions:

• This study identified ten new patients with MCEE deficiency, expanding the known genetic spectrum.
• Misfolding and loss of enzymatic activity are identified as primary molecular defects in MCEE-type MMAuria.
• Structural and functional analyses provide insights into the pathogenicity of MCEE variations.