Deciphering the effect of mutations in MMAA protein causing methylmalonic acidemia-A computational approach

Methylmalonic acidemia (MMA) is a rare genetic disorder affecting multiple body systems. We aimed to investigate the pathogenic mutations in MMAA that are associated with isolated methylmalonic acidemia to identify the structural behavior of MMAA upon mutation. The algorithms such as PredictSNP, iStable, ConSurf, and Align GVGD were employed to analyze the consequence of the mutations. Molecular docking was carried out for the native MMAA, L89P, G274D, and R359G to interpret its interactions with the GDP substrate. The docked complexes were simulated for 200ns aiding GROMACS in apprehending the behavior of MMAA upon mutation and GDP binding. After simulation, cα disruptions were observed using the RMSF plot, which indicated that several regions of mutant MMAAs have highly fluctuated. The gyration and H-bond plots were used to understand the compactness and intermolecular interaction with the GDP molecule. The MDS analysis showed that the mutations L89P, G274D, and R359G are highly unstable even after GDP binding, with the least compactness, fewer H-bonds, and larger conformational cα motions. Our study provided structural and dynamic insights into MMAA protein, which further helps to characterize these mutants and provide potential treatment strategies for MMA patients.

IDENTIFICATION OF A NOVEL MUTATION IN THE MMAA GENE IN A CHINESE BOY WITH ISOLATED METHYLMALONIC ACIDEMIA

Background

Isolated methylmalonic acidemia refers to a group of inborn errors of metabolism characterized by elevated methylmalonic acid concentrations in the blood and urine. It occurs in approximately one to three out of every 100 thousand Chinese newborns. Mutations in the MMAA gene cause isolated methylmalonic acidemia.

Case presentation

A 13-month-old boy was diagnosed with isolated methylmalonic acidemia. We identified two mutations in the MMAA gene in this case: c.491G>A and c.650T>A. The c.491G>A is a novel mutation in the MMAA gene. The boy is a heterozygous carrier of both mutations. The boy was treated with intravenous sodium benzoate and fluids. His sensorium gradually improved and he recovered from the acute illness. Other family members are heterozygous carriers of either mutations but with no symptoms.

Conclusions

We identified a novel c.491G>A mutation in the MMAA gene. Heterozygous carriers of both c.491G>A and c.650T>A mutations are associated with isolated methylmalonic acidemia.

Clinical picture and treatment effects in 5 patients with Methylmalonic aciduria related to MMAA mutations

Introduction

Methylmalonic Aciduria (MMA) is a heterogeneous group of rare diseases leading to accumulation of methylmalonic acid in body fluids. One of the causes of the disease is the methylmalonic aciduria, cblA type (cblA – type MMA), conditioned by a mutation in the MMAA gene, which is essential for the proper functioning of a cofactor of the methylmalonyl-CoA mutase. The symptoms of the disease, depending on the cause, may manifest themselves at different ages. Most patients are sensitive to high doses of hydroxycobalamin, which is associated with better prognosis.

Material and method

The purpose of the study was to retrospectively analyze the clinical picture and effects of treatment of patients with methylmalonic aciduria related to mutation in the MMAA gene.

Results

Five patients with diagnosed cblA – type MMA were presented. At the time of diagnosis the median of age was 18.8 months, but the symptoms had already appeared since infancy, as recurrent vomiting and delayed psychomotor development. Significant excretion of methylmalonic acid in urine and metabolic acidosis traits with significantly increased anionic gap were observed in all patients. All of them were sensitive to the treatment with vitamin B₁₂. The median of therapy duration and observation is 12.2 years. During the treatment, good metabolic control was achieved in all patients, but their cognitive development is delayed. Three patients have renal failure and pharmacologically treated arterial hypertension.

Conclusions

Patients with a mutation in the MMAA gene are sensitive to treatment with hydroxocobalamine, but the inclusion of appropriate treatment does not protect against neurodevelopmental disorders and chronic kidney disease.

Allosteric Regulation of Oligomerization by a B12 Trafficking G-Protein Is Corrupted in Methylmalonic Aciduria

Allosteric regulation of methylmalonyl-CoA mutase (MCM) by the G-protein chaperone CblA is transduced via three "switch" elements that gate the movement of the B₁₂ cofactor to and from MCM. Mutations in CblA and MCM cause hereditary methylmalonic aciduria. Unlike the bacterial orthologs used previously to model disease-causing mutations, human MCM and CblA exhibit a complex pattern of regulation that involves interconverting oligomers, which are differentially sensitive to the presence of GTP versus GDP. Patient mutations in the switch III region of CblA perturb the nucleotide-sensitive distribution of the oligomeric complexes with MCM, leading to loss of regulated movement of B₁₂ to and/or from MCM and explain the molecular mechanism of the resulting disease.

Mutation analysis of genes related to methylmalonic acidemia: identification of eight novel mutations

Methylmalonic acidemia (MMA), an inherited metabolic disease, results from genetic defects in methylmalonyl-CoA mutase or any of the proteins involved in adenosylcobalamin synthesis. This enzyme is classified into several complementation groups and genotypic classes. In this work we explain the biochemical, structural and genetic analysis of 25 MMA patients, from Iran. The diagnosis was established by the measurement of propionylcarnitine in blood using tandem mass spectrometry and confirmed using a gas chromatography-flame ionization detector. Using clinical, biochemical, structural and molecular analyses we identified 15 mut MMA, three cblA, one cblB, and four cblC-deficient patients. Among mutations identified in the MUT gene (MUT) only one, the c.1874A>C (p.D625A) variant, is likely a mut^- mutation. The remaining mutations are probably mut⁰. Here, we present the first molecular analysis of MMA in Iranian patients and have identified eight novel mutations. Four novel mutations (p.D625A, p.R326G, p.V157F, p.F379L) were seen exclusively in patients from northern Iran. One novel splice site mutation (c.2125-3C>G) in MUT and two novel mutation (p.N225M and p.A99P) in the MMAA gene were associated with patients from eastern Iran. The rs184829210 SNP was recognized only in patients with the novel c.958G>A (p.A320T) mutation. This study confirms pathogenesis of deficient enzyme activity in MUT, MMAA, MMAB, and MMACHC as previous observations. These results could act as a basis for the performance of pharmacological therapies for increasing the activity of proteins derived from these mutations.