Recently, Professor Fang Xu's team from the State Key Laboratory of Microbial Technology published a research paper entitled ‘One-pot synthesis of γ-cyclodextrin of high purity from non-food cellulose via an in vitro ATP-free synthetic enzymatic biosystem’ in Carbohydrate Polymers. Niu Kangle, a postdoctoral fellow at the State Key Laboratory of Microbial Technology, was the first author of the paper, and Prof. Fang was the corresponding author, while the State Key Laboratory of Microbial Technology of Shandong University was the first completed unit and the corresponding author affiliation.

γ-Cyclodextrin (γ-CD) is a cyclic oligosaccharide composed of eight glucose molecules linked together via α-1,4-glycosidic bonds. They are characterized by a hydrophilic outer surface and a hydrophobic central cavity capable of encapsulating a wide variety of molecules. As host moieties, the CDs are capable of modifying and enhancing the physical, chemical, and biological properties of the encapsulated guest molecule. Naturally-occurring CDs are mainly of three types: α-, β-, and γ-CD. Compared to α- and β-CDs, γ-CD has the largest central cavity, the highest aqueous solubility, and the most favorable toxicological profile; these features allow a wide range of applications for γ-CD in the pharmaceutical, food, and chemical industries.

The synthesis of γ-CD can be achieved by chemical means or enzymatic catalysis. However, controlling theα-gluco stereoselectivity of the glycosylation reaction is challenging, and the overall process of chemical synthesis involves a large number of complex reactions and processes. Therefore, the development of a method to synthesize γ-CD based on simple and readily available starting materials with high atom economy is of great research interest.

Professor Fang Xu's team has designed two new γ-CD synthesis pathways from the non-food feedstock cellulose via an in vitro adenosine triphosphate (ATP) –free synthetic enzymatic biosystem. Cellulose was employed as the substrate for producing cellobiose, which was subsequently converted to γ-CD via a cascade reaction utilizing five enzymes. A stoichiometric conversion of cellulose to γ-CD was achieved by adding the synthesis module for glucose-1-phosphate(G-1-P) and optimizing the reaction conditions. A process for producing γ-CD from cellulose was established in this study, which yielded γ-CD of >90% purity. This study presents a strategy for improving the economic considerations associated with cellulose utilization and broadens the scope of processes that could be employed in next-generation lignocellulosic biorefineries.

This work was supported by the National Key Research and Development Program of China, the National Natural Science Foundation of China and the Qingdao Postdoctoral Application Research Project. Core Facilities for Life and Environmental Sciences of Shandong University provided important support for this work.