Glucosamine, GlcN in short, the main component of proteoglycans and glycoproteins, exists in various organisms and can be translated into glucose-6-phosphate inside the cell through amination. N-acetyl-d-glucosamine (GlcNAc) is widely used in medicine, food, daily chemical and other fields. Traditionally, the GlcNAc is produced by acid hydrolysis, using the chitin of shrimps and crabs as raw material. The reaction requires concentrated acid and high temperature conditions, which will cause serious environmental pollution, and the equipment requirement is strict and the production cost is high. With the rapid development of metabolic engineering and synthetic biology, biological fermentation method used in the industrial yield is becoming more and more mature. The glucose is used as a raw material to directly convert into glucosamine, which has the advantages of low material cost, simple extraction, high purity of the product, less pollution and so on.
Glucosamine synthase (GLS) is the key enzyme of GlcN biosynthesis, which can catalyze fructose-6-phosphate to generate GlcN-6-P with the glutamine as amino donor. This is the first rate-limiting reaction in the synthesis pathway of GlcN, and GLS is seriously affected by the product inhibition effect of the metabolite GlcN-6-P. Therefore, GlcN-6-P cannot be largely accumulated in the normal metabolic synthesis. In order to reduce the inhibition of the product, co-expression of glucosamine acetyltransferase gene is usually used in the E. coli system to convert the GlcN-6-P in the metabolic system into GlcNAc-6-P with a small stimulation Both the product GlcN-6-P and GlcNAc-6-P can be transferred from intracellular to extracellular, and be dephosphorylated into GlcNa and GlcNAc respectively, while GlcNAc can be converted into GlcN through deacetylation under the acidic condition. The low biosynthetic ability and poor tolerance to the product of GLS are the main reasons that limit the increase in the yield. Although strains used in current industrial yield have far exceeded the level, most of which were optimized through metabolic engineering and fermentation control, but the literature analysis shows that one focus of the transformation is glucosamine synthase.
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