New variants of AADC deficiency expand the knowledge of enzymatic phenotypes

Arch Biochem Biophys. 2020 Mar 30:682:108263. doi: 10.1016/j.abb.2020.108263. Epub 2020 Jan 15.

Abstract

AADC deficiency is a rare genetic disease caused by mutations in the gene of aromatic amino acid decarboxylase, the pyridoxal 5'-phosphate dependent enzyme responsible for the synthesis of dopamine and serotonin. Here, following a biochemical approach together with an in silico bioinformatic analysis, we present a structural and functional characterization of 13 new variants of AADC. The amino acid substitutions are spread over the entire protein from the N-terminal (V60A), to its loop1 (H70Y and F77L), to the large domain (G96R) and its various motifs, i.e. loop2 (A110E), or a core β-barrel either on the surface (P210L, F251S and E283A) or in a more hydrophobic milieu (L222P, F237S and W267R) or loop3 (L353P), and to the C-terminal domain (R453C). Results show that the β-barrel variants exhibit a low solubility and those belonging to the surface tend to aggregate in their apo form, leading to the identification of a new enzymatic phenotype for AADC deficiency. Moreover, five variants of residues belonging to the large interface of AADC (V60A, G96R, A110E, L353P and R453C) are characterized by a decreased catalytic efficiency. The remaining ones (H70Y and F77L) present features typical of apo-to-holo impaired transition. Thus, defects in catalysis or in the acquirement of the correct holo structure are due not only to specific local domain effects but also to long-range effects at either the protein surface or the subunit interface. Altogether, the new characterized enzymatic phenotypes represent a further step in the elucidation of the molecular basis for the disease.

Keywords: AADC deficiency variants; Aromatic amino acid decarboxylase deficiency; Enzymology; Protein chemistry; Pyridoxal 5′-phosphate enzymes; Structure and function relationship.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Algorithms
  • Amino Acid Metabolism, Inborn Errors / genetics*
  • Amino Acid Motifs
  • Aromatic-L-Amino-Acid Decarboxylases / chemistry
  • Aromatic-L-Amino-Acid Decarboxylases / deficiency*
  • Aromatic-L-Amino-Acid Decarboxylases / genetics
  • Catalysis
  • Computational Biology
  • Escherichia coli
  • Genetic Variation
  • Humans
  • Kinetics
  • Magnetic Resonance Spectroscopy
  • Mutagenesis, Site-Directed
  • Mutation
  • Phenotype*
  • Protein Domains
  • Scattering, Radiation
  • Solubility
  • Spectrophotometry
  • Structure-Activity Relationship
  • Temperature

Substances

  • Aromatic-L-Amino-Acid Decarboxylases
  • DDC protein, human

Supplementary concepts

  • Aromatic amino acid decarboxylase deficiency