Enzymatic production of N-acetylneuraminic acid: advances and perspectives

N-Acetyl-d-neuraminic acid (NeuAc), a well-known and well-studied sialic acid, is found in cell surface glycolipids and glycoproteins, where it performs a variety of biological functions. The use of NeuAc as a nutraceutical for infant brain development and as an intermediate for pharmaceutical production demands its production on an industrial scale. Natural extraction, chemical synthesis, enzymatic synthesis, and biosynthesis are the methods used for NeuAc production. Among these methods, enzymatic synthesis using N-acetyl-glucosamine (GlcNAc) 2-epimerase (AGE) for epimerization and N-acetyl-d-neuraminic acid lyase (NAL) for aldol condensation, has been reported to produce NeuAc with high production efficiency. In this review, we discuss advances in the two-step enzymatic synthesis of NeuAc using pyruvate and GlcNAc as substrates. The major challenges in producing NeuAc with high yield are highlighted, including multiple parameter-dependent processes, undesirable reversibility, and diminished solubility of AGEs and NALs. Further, different strategies applied to overcome the limitations of the two-step enzymatic production are discussed, such as pyruvate concentration and temperature shift during the process to increase conversion yield, use of mathematical and computational simulations for process optimization, enzyme engineering to make enzymes highly efficient, and the use of tags and chaperones to increase enzyme solubility. We suggest future directions and the strategies that can be followed to improve enzymatic synthesis of NeuAc.