Asn-150 of Murine Erythroid 5-Aminolevulinate Synthase Modulates the Catalytic Balance between the Rates of the Reversible Reaction

Nutritional Factors That Affect the Formation of 5-Aminolevulinic Acid, a Key Intermediate of Heme Biosynthesis

5-Aminolevulinic acid (ALA) is a key intermediate of heme biosynthesis, which is an essential component of the respiratory chain. Therefore, nutrients that affect ALA biosynthesis eventually affect ATP production, which is the basis of mitochondrial function. Although the effects of various non-nutrient components that affect ALA after biosynthesis have been reported, there are few reports on the effects of dietary amino acids/protein on ALA formation and the effects of dietary vitamins that are involved in amino acid metabolism. In mitochondria, ALA is synthesized from succinyl-CoA and glycine by the pyridoxal phosphate-dependent enzyme ALA synthase [EC 2.3.1.37]. In this study, the effects of dietary amino acids/protein and vitamins on the amount of ALA synthesized were investigated using mice, rats, and cultured cells. Amounts of ALA in plasma and urine, and porphyrins in plasma increased with increasing protein intake. Vitamin B₁ insufficiency did not affect ALA synthesis. Vitamin B₆ insufficiency increased the amount of ALA synthesized, while niacin deficiency markedly reduced ALA synthesis. Thus, for heme synthesis, an essential biological substance for life, the amounts of amino acids, as well as the pathways metabolizing amino acids to glycine and succinyl-CoA are very important. Specifically, it is important that niacin is associated with the formation of glycine and succinyl-CoA from amino acids.

Challenges and opportunities of bioprocessing 5-aminolevulinic acid using genetic and metabolic engineering: a critical review

5-Aminolevulinic acid (5-ALA), a non-proteinogenic five-carbon amino acid, has received intensive attentions in medicine due to its approval by the US Food and Drug Administration (FDA) for cancer diagnosis and treatment as photodynamic therapy. As chemical synthesis of 5-ALA performed low yield, complicated processes, and high cost, biosynthesis of 5-ALA via C4 (also called Shemin pathway) and C5 pathway related to heme biosynthesis in microorganism equipped more advantages. In C4 pathway, 5-ALA is derived from condensation of succinyl-CoA and glycine by 5-aminolevulic acid synthase (ALAS) with pyridoxal phosphate (PLP) as co-factor in one-step biotransformation. The C5 pathway involves three enzymes comprising glutamyl-tRNA synthetase (GltX), glutamyl-tRNA reductase (HemA), and glutamate-1-semialdehyde aminotransferase (HemL) from α-ketoglutarate in TCA cycle to 5-ALA and heme. In this review, we describe the recent results of 5-ALA production from different genes and microorganisms via genetic and metabolic engineering approaches. The regulation of different chassis is fine-tuned by applying synthetic biology and boosts 5-ALA production eventually. The purification process, challenges, and opportunities of 5-ALA for industrial applications are also summarized.

5-Aminolevulinate synthase catalysis: The catcher in heme biosynthesis

5-Aminolevulinate (ALA) synthase (ALAS), a homodimeric pyridoxal-5'-phosphate (PLP)-dependent enzyme, catalyzes the first step of heme biosynthesis in metazoa, fungi and α-proteobacteria. In this review, we focus on the advances made in unraveling the mechanism of the ALAS-catalyzed reaction during the past decade. The interplay between the PLP cofactor and the protein moiety determines and modulates the multi-intermediate reaction cycle of ALAS, which involves the decarboxylative condensation of two substrates, glycine and succinyl-CoA. Substrate binding and catalysis are rapid, and product (ALA) release dominates the overall ALAS kinetic mechanism. Interconversion between a catalytically incompetent, open conformation and a catalytically competent, closed conformation is linked to ALAS catalysis. Reversion to the open conformation, coincident with ALA dissociation, defines the slowest step of the reaction cycle. These findings were further substantiated by introducing seven mutations in the16-amino acid loop that gates the active site, yielding an ALAS variant with a greatly increased rate of catalytic turnover and heightened specificity constants for both substrates. Recently, molecular dynamics (MD) simulation analysis of various dimeric ALAS forms revealed that the seven active site loop mutations caused the proteins to adopt different conformations. In particular, the emergence of a β-strand in the mutated loop, which interacted with two preexisting β-strands to form an anti-parallel three-stranded β-sheet, conferred the murine heptavariant with a more stable open conformation and prompted faster product release than wild-type mALAS2. Moreover, the dynamics of the mALAS2 active site loop anti-correlated with that of the 35 amino acid C-terminal sequence. This led us to propose that this C-terminal extension, which is absent in prokaryotic ALASs, finely tunes mammalian ALAS activity. Based on the above results, we extend our previous proposal to include that discovery of a ligand inducing the mammalian C-terminal extension to fold offers a good prospect for the development of a new drug for X-linked protoporphyria and/or other porphyrias associated with enhanced ALAS activity and/or porphyrin accumulation.

Macromolecular crowders and osmolytes modulate the structural and catalytic properties of alkaline molten globular 5-aminolevulinate synthase

Tertiary structure, solvation and kinetic properties of the catalytically active aminolevulinate synthase molten globule are modulated by crowders or osmolytes.