Crystal structure of human branched-chain α-ketoacid dehydrogenase and the molecular basis of multienzyme complex deficiency in maple syrup urine disease

1. Comparisons of the activity and kinetics of the branched-chain 2-oxo acid dehydrogenase in cultured skin fibroblasts from normal and classical maple-syrup-urine-disease (MSUD) subjects provide a kinetic explanation for the enzyme defect. 2. In the intact cell assays, normal fibroblasts demonstrated hyperbolic kinetics with 3-methyl-2-oxo[1-14C]butyrate as a substrate. Intact fibroblasts from four classical MSUD patients showed no decarboxylation over a substrate concentration range of 0.25 to 5.0 mM, and thiamin (4 mM) was without effect. 3. The overall reaction of the multienzyme complex was efficiently reconstituted by using a disrupted-cell system. Normals again showed typical hyperbolic kinetics at the 2-oxo acid concentrations of 0.1 to 5 mM. The Vmax. and apparent Km values were 0.10 +/- 0.02 m-unit/mg of protein and 0.05-0.1 mM respectively, with 3-methyl-2-oxobutyrate. In contrast, classical MSUD patients exhibited sigmoidal kinetics (Hill coefficient, 2.5) with activity approaching 40-60% of the normal value at 5 mM substrate. The K0.5 values from the Hill plots for MSUD patients were 4-7 mM. 4. The E1 (branched-chain 2-oxo acid decarboxylase) component of the multienzyme complex was measured in disrupted-particulate preparations. Normals again showed hyperbolic kinetics with the 2-oxo acid, whereas MSUD preparations exhibited sigmoidal kinetics with the activity of E1 strictly dependent on substrate concentration. Apparent Km or K0.5 were 0.1 and 1.0 mM for normal and MSUD subjects respectively. 5. Measurements of E2 (dihydrolipoyl transacylase) and E3 (dihydrolipoyl dehydrogenase) in MSUD preparations showed them to be in the normal range. 6. The above data suggest a defect in the E1 step of branched-chain 2-oxo acid dehydrogenase in classical MSUD patients.

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Four novel mutations of the BCKDHA, BCKDHB and DBT genes in Iranian patients with maple syrup urine disease

Journal of Pediatric Endocrinology and Metabolism ◽

10.1515/jpem-2017-0305 ◽

2018 ◽

Vol 31 (2) ◽

pp. 205-212 ◽

Cited By ~ 2

Author(s):

Monica Zeynalzadeh ◽

Alireza Tafazoli ◽

Azadeh Aarabi ◽

Morteza Moghaddassian ◽

Farah Ashrafzadeh ◽

...

Keyword(s):

Maple Syrup Urine Disease ◽

Energy Levels ◽

Clinical Manifestations ◽

Autosomal Recessive Disorder ◽

Strong Correlations ◽

Novel Mutations ◽

Maple Syrup ◽

Urine Disease ◽

Branched Chain ◽

Ketoacid Dehydrogenase

Abstract Background: Maple syrup urine disease (MSUD) is a rare metabolic autosomal recessive disorder caused by dysfunction of the branched-chain α-ketoacid dehydrogenase (BCKDH) complex. Mutations in the BCKDHA, BCKDHB and DBT genes are responsible for MSUD. The current study analyzed seven Iranian MSUD patients genetically and explored probable correlations between their genotype and phenotype. Methods: The panel of genes, including BCKDHA, BCKDHB and DBT, was evaluated, using routine the polymerase chain reaction (PCR)-sequencing method. In addition, protein modeling (homology and threading modeling) of the deduced novel mutations was performed. The resulting structures were then analyzed, using state-of-the-art bioinformatics tools to better understand the structural and functional effects caused by mutations. Results: Seven mutations were detected in seven patients, including four novel pathogenic mutations in BCKDHA (c.1198delA, c.629C>T), BCKDHB (c.652C>T) and DBT (c.1150A>G) genes. Molecular modeling of the novel mutations revealed clear changes in the molecular energy levels and stereochemical traits of the modeled proteins, which may be indicative of strong correlations with the functional modifications of the genes. Structural deficiencies were compatible with the observed phenotypes. Conclusions: Any type of MSUD can show heterogeneous clinical manifestations in different ethnic groups. Comprehensive molecular investigations would be necessary for differential diagnosis.

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Maple Syrup Urine Disease in a Central Indiana Hereford Herd

Case Reports in Veterinary Medicine ◽

10.1155/2015/204037 ◽

2015 ◽

Vol 2015 ◽

pp. 1-4 ◽

Cited By ~ 1

Author(s):

Mark E. Robarge ◽

Jonathan E. Beever ◽

Stephen D. Lenz ◽

Christopher J. Lynch ◽

William L. Wigle

Keyword(s):

Maple Syrup Urine Disease ◽

Index Case ◽

Clinical Signs ◽

Maple Syrup ◽

Hereford Cattle ◽

Urine Disease ◽

Branched Chain ◽

Ketoacid Dehydrogenase ◽

Dehydrogenase Complex ◽

T Haplotype

Maple syrup urine disease (MSUD) and further cases were identified in herd mates of a small Hereford herd in Indiana based on history, clinical signs, microscopic lesions, and biochemical and genetic testing. This aminoacidopathy has been diagnosed in polled Shorthorn, polled Hereford, and Hereford cattle in Australia, Uruguay, Argentina, and Canada and is the result of a mutation of the branched-chain alpha-ketoacid dehydrogenase complex. The Indiana index calf case was confirmed by showing the classic accumulation of ketoacids in liver that results from a defect in the E1-alpha subunit (248 C/T haplotype) in the mitochondrial branched-chainα-ketoacid dehydrogenase complex. The presence of the mutation was confirmed in the index case, the dam, and four related herd mates that represent the first confirmed cases of bovine MSUD mutation in United States cattle.

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Hereditary characteristics of the S339L mutation in a patient with maple syrup urine disease in Vietnam

ACADEMIA JOURNAL OF BIOLOGY ◽

10.15625/2615-9023/v42n2.14913 ◽

2020 ◽

Vol 42 (2) ◽

Author(s):

Nguyen Thi Thu Huong ◽

Vu Chi Dung ◽

Nguyen Thi Thanh Ngan ◽

Nguyen Kim Thoa ◽

Nguyen Huy Hoang

Keyword(s):

Amino Acids ◽

Maple Syrup Urine Disease ◽

Neurological Complications ◽

Scientific Basis ◽

Homozygous Mutation ◽

Maple Syrup ◽

Urine Disease ◽

Bckdhb Gene ◽

Branched Chain ◽

Ketoacid Dehydrogenase

Maple syrup urine disease (MSUD) is an autosomal recessive inherited metabolic disorder caused by malfunction of the branched-chain α-ketoacid dehydrogenase complex (BCKDH). This enzyme complex participates in the catalyzing metabolisms of the branched-chain α-ketoacids, the second step of the degradation of branched-chain amino acids. Impaired activities of the BCKAD complex lead to an increase of the levels of branched- chain amino acid such as leucine, valine, and isoleucine in the blood. In children with maple syrup urine disease, catalysis of the metabolisms of some amino acids failed to be implemented, leading to an accumulation of the amino acids which has been shown as one of the causes of neurological complications, intellectual disabilities, and nervous paralysis or even death. Pathogenic mutations normally occur in BCKDHA, BCKDHB, DBT and DLD genes which encode the E1α, E1β, and E2 subunits of the BCKDH complex. In the present study, a homozygous mutation in the BCKDHB gene (c. 1016C>T) in a pediatric patient with MSUD diagnosed at The National Hospital of Pediatrics was identified using whole exome and Sanger sequencing methods. As a result, the inheritance of the homozygous mutation related to MSUD in BCKDHB gene within the pedigree of the patient’s family was determined. The results indicated that the mutation in the BCKDHB gene was inherited from both of the patient’s parents. In addition, this finding provides an important scientific basis to researches on MSUD in the Vietnamese population.

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Investigation of L-Carnitine Concentrations in Treated Patients with Maple Syrup Urine Disease

Journal of Pediatric Genetics ◽

10.1055/s-0039-1691789 ◽

2019 ◽

Vol 08 (03) ◽

pp. 133-136

Author(s):

Burcu Kumru ◽

Burcu Oztürk Hismi

Keyword(s):

Maple Syrup Urine Disease ◽

Antioxidant Properties ◽

Maple Syrup ◽

Atp Production ◽

Control Subjects ◽

Healthy Control ◽

Urine Disease ◽

Branched Chain ◽

Ketoacid Dehydrogenase

AbstractMaple syrup urine disease (MSUD), also known as branched-chain α ketoaciduria, is a metabolic disorder caused by an inborn deficiency in the activity of the branched-chain α-ketoacid dehydrogenase complex. Severe neurological damage occurs in most patients with MSUD although the exact mechanism of neurotoxicity still remains unknown. Studies have suggested that neuropathology in patients with MSUD may be related to oxidative stress. L-carnitine mediates the transport of fatty acids into the mitochondria that are required for β-oxidation and ATP production. Along with the important roles it plays in lipid metabolism, L-carnitine also protects tissues from oxidative damage through its antioxidant properties. The study included a total of 15 patients with MSUD who attended regular follow-up visits, and 15 age-matched healthy control subjects, and aimed to investigate L-carnitine levels in treated patients with MSUD and healthy control subjects. L-carnitine levels were found to be significantly lower in the patient group than in the healthy controls. No significant correlation was identified between the plasma branched-chain amino acids leucine, isoleucine, valine, and L-carnitine levels. Patients with MSUD can be treated with adjuvant therapy with L-carnitine supplementation.

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