TY - JOUR
T1 - A novel compound heterozygous genotype associated with aromatic amino acid decarboxylase deficiency
T2 - Clinical aspects and biochemical studies
AU - Montioli, Riccardo
AU - Battini, Roberta
AU - Paiardini, Alessandro
AU - Tolve, Manuela
AU - Bertoldi, Mariarita
AU - Carducci, Carla
AU - Leuzzi, Vincenzo
AU - Borri Voltattorni, Carla
PY - 2019/6
Y1 - 2019/6
N2 - Aromatic amino acid decarboxylase (AADC) deficiency is a rare autosomal neurometabolic disorder caused by a deficit of AADC, a pyridoxal 5′-phosphate (PLP)-dependent enzyme, which catalyzes the synthesis of dopamine and serotonin. While many studies have highlighted the molecular defects of the homozygous pathogenic variants, so far only a study investigated heterozygous variants at protein level. Here, we report a clinical case of one AADC deficiency compound heterozygous patient bearing the A91V mutation and the novel C410G mutation. To elucidate its enzymatic phenotype, the A91V and C410G homodimers were first expressed in Escherichia coli, purified and characterized. Although both apo variants display an unaltered overall tertiary structure, they show a ̴ 20-fold decreased PLP binding affinity. The C410G mutation only causes a ̴ 4-fold decrease of the catalytic efficiency, while the A91V mutation causes a 1300-fold decrease of the kcat/Km, and changes in the holoAADC consisting in a marked alteration of the tertiary structure and the coenzyme microenvironment. Structural analyses of these mutations are in agreement with these data. Unfortunately, the C410G/A91V heterodimer was constructed, expressed and purified in rather modest amount. Anyway, measurements of decarboxylase activity indicate that its putative kcat value is lower than that predicted by averaging the kcat values of the two parental enzymes. This indicates a negative interallelic complementation between the C410G and A91V monomers. Overall, this study allowed to relate the clinical to the enzymatic phenotype of the patient and to extend knowledge in the clinical and molecular pathogenesis of AADC deficiency.
AB - Aromatic amino acid decarboxylase (AADC) deficiency is a rare autosomal neurometabolic disorder caused by a deficit of AADC, a pyridoxal 5′-phosphate (PLP)-dependent enzyme, which catalyzes the synthesis of dopamine and serotonin. While many studies have highlighted the molecular defects of the homozygous pathogenic variants, so far only a study investigated heterozygous variants at protein level. Here, we report a clinical case of one AADC deficiency compound heterozygous patient bearing the A91V mutation and the novel C410G mutation. To elucidate its enzymatic phenotype, the A91V and C410G homodimers were first expressed in Escherichia coli, purified and characterized. Although both apo variants display an unaltered overall tertiary structure, they show a ̴ 20-fold decreased PLP binding affinity. The C410G mutation only causes a ̴ 4-fold decrease of the catalytic efficiency, while the A91V mutation causes a 1300-fold decrease of the kcat/Km, and changes in the holoAADC consisting in a marked alteration of the tertiary structure and the coenzyme microenvironment. Structural analyses of these mutations are in agreement with these data. Unfortunately, the C410G/A91V heterodimer was constructed, expressed and purified in rather modest amount. Anyway, measurements of decarboxylase activity indicate that its putative kcat value is lower than that predicted by averaging the kcat values of the two parental enzymes. This indicates a negative interallelic complementation between the C410G and A91V monomers. Overall, this study allowed to relate the clinical to the enzymatic phenotype of the patient and to extend knowledge in the clinical and molecular pathogenesis of AADC deficiency.
KW - AADC deficiency
KW - Dopa decarboxylase
KW - Heterozygous mutation
KW - Interallelic complementation
KW - Pyridoxal 5′-phosphate
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U2 - 10.1016/j.ymgme.2019.05.004
DO - 10.1016/j.ymgme.2019.05.004
M3 - Article
C2 - 31104889
AN - SCOPUS:85065612038
VL - 127
SP - 132
EP - 137
JO - Molecular Genetics and Metabolism
JF - Molecular Genetics and Metabolism
SN - 1096-7192
IS - 2
ER -