The Functional Characteristics and Soluble Expression of Saffron CsCCD2

Recent Advancements in the Biomanufacturing of Crocetin and Crocins: Key Enzymes and Metabolic Engineering

Crocetin and crocins are high-value apocarotenoids recognized for their role as food colorants as well as for their numerous industrial and therapeutic applications. Biotechnological platforms have the potential to replace traditional plant-based extraction of these compounds with a more sustainable approach. This review first introduced the catalytic characteristics of key enzymes involved in the biosynthetic pathway of crocetin and crocins, including carotenoid cleavage dioxygenases, aldehyde dehydrogenases, and uridine diphosphate glycosyltransferases. Next, we highlighted advanced metabolic engineering strategies aimed at enhancing crocetin and crocin production, such as increasing the pool of precursors and cofactors, protein mining and engineering, tuning protein expression, biosensor, genomic integration, and process optimization. Finally, the paper proposed potential strategies and tools associated with further boosting the heterologous production of crocetin and crocins to meet commercial-scale demands.

Construction of a high-efficiency GjCCD4a mutant and its application for de novo biosynthesis of five crocins in Escherichia coli

Crocins are bioactive natural products that rarely exist in plants. High costs and resource shortage severely limit its development and application. Synthetic biology studies on crocins are of considerable global interest. However, the lack of high-efficiency genetic tools and complex cascade biocatalytic systems have substantially hindered progress in crocin biosynthesis-related research. Based on mutagenesis, a high-efficiency GjCCD4a mutant (N212m) was constructed with a catalytic efficiency that was 25.08-fold higher than that of the wild-type. Solubilized GjCCD4a was expressed via fusion with an MBP tag. Moreover, N212m and ten other genes were introduced into Escherichia coli for the de novo biosynthesis of five crocins. The engineered E57 strain produced crocins III and V with a total yield of 11.50 mg/L, and the E579 strain produced crocins I-V with a total output of 8.43 mg/L at shake-flask level. This study identified a marvelous genetic element (N212m) for crocin biosynthesis and achieved its de novo biosynthesis in E. coli using glucose. This study provides a reference for the large-scale production of five crocins using E. coli cell factories.

Research Progress in Heterologous Crocin Production

Crocin is one of the most valuable components of the Chinese medicinal plant Crocus sativus and is widely used in the food, cosmetics, and pharmaceutical industries. Traditional planting of C. sativus is unable to fulfill the increasing demand for crocin in the global market, however, such that researchers have turned their attention to the heterologous production of crocin in a variety of hosts. At present, there are reports of successful heterologous production of crocin in Escherichia coli, Saccharomyces cerevisiae, microalgae, and plants that do not naturally produce crocin. Of these, the microalga Dunaliella salina, which produces high levels of β-carotene, the substrate for crocin biosynthesis, is worthy of attention. This article describes the biosynthesis of crocin, compares the features of each heterologous host, and clarifies the requirements for efficient production of crocin in microalgae.