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

Abstract

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.

Keywords: 5-aminolevulinic acid; Bioprocessing, metabolic engineering; C4 and C5 pathway; Heme; Photodynamic therapy.

Fig. 1

The C4 pathway for 5-ALA and heme synthesis. The up and down arrows beside the gene indicate the up- or down-regulation of the gene which can increase 5-ALA accumulation

Fig. 2

The C5 pathway for 5-ALA and heme synthesis. The up and down arrows beside the gene indicate the up- or down-regulation of the gene which can increase 5-ALA accumulation

Fig. 3

ALA ion exchange process. The resin is filled in the chromatography to adsorb 5-ALA and then washed out by eluent