Molecular Identification of Hydroxylysine Kinase and of Ammoniophospholyases Acting on 5-Phosphohydroxy-l-lysine and Phosphoethanolamine

• Published in: The Journal of biological chemistry 2012-03, Vol.287 (10), p.7246-7255
• Main Authors: Veiga-da-Cunha, Maria, Hadi, Farah, Balligand, Thomas, Stroobant, Vincent, Van Schaftingen, Emile
• Format: Article
• Language: English
• Subjects: Ammoniophospholyases; Animals; Bacteria - enzymology; Bacteria - genetics; Bacterial Proteins - chemistry; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Bipolar Disorder - enzymology; Bipolar Disorder - genetics; Bipolar Disorders; Comparative Genomics; Ethanolamines - chemistry; Ethanolamines - metabolism; Genome, Bacterial - physiology; Genome, Human - physiology; Humans; Hydroxylysine; Hydroxylysine - analogs & derivatives; Hydroxylysine - chemistry; Hydroxylysine - metabolism; Inborn Errors of Metabolism; Metabolism; Molecular Identification; Mutation; Phosphatidylethanolamine; Phosphoethanolamine; Pyridoxal Phosphate; Schizophrenia; Schizophrenia - enzymology; Schizophrenia - genetics; Sequence Homology, Amino Acid; Transaminases - chemistry; Transaminases - genetics; Transaminases - metabolism
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M111.323485

The purpose of the present work was to identify the catalytic activity of AGXT2L1 and AGXT2L2, two closely related, putative pyridoxal-phosphate-dependent enzymes encoded by vertebrate genomes. The existence of bacterial homologues (40–50% identity with AGXT2L1 and AGXT2L2) forming bi- or tri-functional proteins with a putative kinase belonging to the family of aminoglycoside phosphotransferases suggested that AGXT2L1 and AGXT2L2 acted on phosphorylated and aminated compounds. Vertebrate genomes were found to encode a homologue (AGPHD1) of these putative bacterial kinases, which was therefore likely to phosphorylate an amino compound bearing a hydroxyl group. These and other considerations led us to hypothesize that AGPHD1 corresponded to 5-hydroxy-l-lysine kinase and that AGXT2L1 and AGXT2L2 catalyzed the pyridoxal-phosphate-dependent breakdown of phosphoethanolamine and 5-phosphohydroxy-l-lysine. The three recombinant human proteins were produced and purified to homogeneity. AGPHD1 was indeed found to catalyze the GTP-dependent phosphorylation of 5-hydroxy-l-lysine. The phosphorylation product made by this enzyme was metabolized by AGXT2L2, which converted it to ammonia, inorganic phosphate, and 2-aminoadipate semialdehyde. AGXT2L1 catalyzed a similar reaction on phosphoethanolamine, converting it to ammonia, inorganic phosphate, and acetaldehyde. AGPHD1 and AGXT2L2 are likely to be the mutated enzymes in 5-hydroxylysinuria and 5-phosphohydroxylysinuria, respectively. The high level of expression of AGXT2L1 in human brain, as well as data in the literature linking AGXT2L1 to schizophrenia and bipolar disorders, suggest that these diseases may involve a perturbation of brain phosphoethanolamine metabolism. AGXT2L1 and AGXT2L2, the first ammoniophospholyases to be identified, belong to a family of aminotransferases acting on ω-amines. Vertebrate genomes encode AGXT2L1 and AGXT2L2, two related, pyridoxal-phosphate dependent enzymes of unknown function. Comparison with bacterial genomes suggested that AGXT2L1 and AGXT2L2 are ammoniophospholyases functionally related with AGPHD1. The three recombinant proteins were produced and studied. AGXT2L1 is O-phosphoethanolamine phospholyase; AGXT2L2 is 5-phosphohydroxy-l-lysine phospholyase; AGPHD1 is 5-hydroxylysine kinase. These molecular identifications will help explain some specific neurometabolic diseases.