Expanding the application range of the κ‑carrageenase OUC-FaKC16A when preparing oligosaccharides from κ-carrageenan and furcellaran

Engineering the Non-catalytic Domain to Enhance Catalytic Activity and Thermal Stability of a Nκ2-Producing κ-Carrageenase

κ-Carrageenases play an important role in achieving the high-value utilization of carrageenan polysaccharides. They can be used in the preparation of even-numbered κ-neocarrageenan oligosaccharides by degrading κ-carrageenan (KC). We previously identified and characterized a κ-carrageenase, CaKC16B, with high specificity for producing a single κ-neocarrabiose. It can produce a single κ-neocarrabiose from degrading KC. However, they also exhibited poor thermal stability and catalytic efficiency. To improve these properties, we introduced noncatalytic domains (nonCDs) from a heat-resistant κ-carrageenase, MtKC16A, into the C-terminus of CaKC16B to construct CaKC16BUN and CaKC16BUNB. Compared to the original CaKC16B, both of them exhibited improved enzymatic properties, including optimal reaction temperature, thermal stability, substrate affinity, and catalytic efficiency. Remarkably, the kcat/Km values of 16BUN and 16BUNB increased by 127 and 290 times, respectively. Importantly, the addition of nonCDs did not alter the final products of degrading KC, retaining the high product specificity of CaKC16B. Interestingly, the addition of nonCDs changed CaKC16B's substrate specificity for hydrolyzing KC and βκ-carrageenan, with mutants exhibiting higher relative activity for βκ-carrageenan. We further observed through biolayer interferometry that the binding and dissociation process between MtUN nonCD and βκ-carrageenan is faster compared to that of KC. This may explain the change in the substrate specificity observed in the mutants of CaKC16B.

Simultaneous One-Step Preparation of β/κ-Carrapentaose and 3,6-Anhydro-D-galactose by Cascading κ-Carrageenase and an Exo-α-3,6-Anhydro-D-galactosidase

Carrageenan oligosaccharides have shown promising bioavailability and possess a variety of physiological activities, making them highly suitable for use in the food, pharmaceutical, and agricultural industries. The preferred method for producing carrageenan oligosaccharides is using various carrageenolytic enzymes, as it offers mild reaction conditions, high efficiency, and product specificity. However, there is still a lack of specific applications for using these enzymes to prepare odd-numbered carrageenan-oligosaccharides (OCOSs). Our previous research identified a more convenient route for simultaneously preparing OCOSs and 3,6-anhydro-D-galactose (D-AHG) using only two types of carrageenolytic enzymes: κ-carrageenase and exo-α-3,6-anhydro-D-galactosidase (D-ADAGase). In this study, we utilized a CipA-based self-assembly system to cascade κ-carrageenase CaKC16A and D-ADAGase ZuGH129A for one-step preparation of β/κ-carrapentaose, G-(DA-G4S)2, and D-AHG from degrading β/κ-carrageenan. This self-assembled enzyme, namely CipA-CaKC16A-ZuGH129A, can be easily obtained through a simple centrifugation process. The final optimized enzymatic process produced 0.74 g/L G-(DA-G4S)2 and 0.13 g/L D-AHG. This cascade system of different types of carrageenolytic enzymes has the potential to achieve the preparation of various types of carrageenan oligosaccharides.

Directed preparation of algal oligosaccharides with specific structures by algal polysaccharide degrading enzymes

Seaweed polysaccharides have a wide range of sources and rich content, with various biological activities such as anti-inflammatory, anti-tumor, anticoagulant, and blood pressure lowering. They can be applied in fields such as food, agriculture, and medicine. However, the poor solubility of macromolecular seaweed polysaccharides limits their further application. Reports have shown that some biological activities of seaweed oligosaccharides are more extensive and superior to that of seaweed polysaccharides. Therefore, reducing the degree of polymerization of polysaccharides will be the key to the high value utilization of seaweed polysaccharide resources. There are three main methods for degrading algal polysaccharides into algal oligosaccharides, physical, chemical and enzymatic degradation. Among them, enzymatic degradation has been a hot research topic in recent years. Various types of algal polysaccharide hydrolases and related glycosidases are powerful tools for the preparation of algal oligosaccharides, including α-agarases, β-agaroses, α-neoagarose hydrolases and β-galactosidases that are related to agar, κ-carrageenases, ι-carrageenases and λ-carrageenases that are related to carrageenan, β-porphyranases that are related to porphyran, funoran hydrolases that are related to funoran, alginate lyases that are related to alginate and ulvan lyases related to ulvan. This paper describes the bioactivities of agar oligosaccharide, carrageenan oligosaccharide, porphyran oligosaccharide, funoran oligosaccharide, alginate oligosaccharide and ulvan oligosaccharide and provides a detailed review of the progress of research on the enzymatic preparation of these six oligosaccharides. At the same time, the problems and challenges faced are presented to guide and improve the preparation and application of algal oligosaccharides in the future.

Systematic review on carrageenolytic enzymes: From metabolic pathways to applications in biotechnology

Carrageenan, the major carbohydrate component of some red algae, is an important renewable bioresource with very large annual outputs. Different types of carrageenolytic enzymes in the carrageenan metabolic pathway are potentially valuable for the production of carrageenan oligosaccharides, biofuel, and other chemicals obtained from carrageenan. However, these enzymes are not well-developed for oligosaccharide or biofuel production. For further application, comprehensive knowledge of carrageenolytic enzymes is essential. Therefore, in this review, we first summarize various carrageenolytic enzymes, including the recently discovered β-carrageenase, carrageenan-specific sulfatase, exo-α-3,6-anhydro-D-galactosidase (D-ADAGase), and exo-β-galactosidase (BGase), and describe their enzymatic characteristics. Subsequently, the carrageenan metabolic pathways are systematically presented and applications of carrageenases and carrageenan oligosaccharides are illustrated with examples. Finally, this paper discusses critical aspects that can aid researchers in constructing cascade catalytic systems and engineered microorganisms to efficiently produce carrageenan oligosaccharides or other value-added chemicals through the degradation of carrageenan. Overall, this paper offers a comprehensive overview of carrageenolytic enzymes, providing valuable insights for further exploration and application of these enzymes.

Comparative Study on Enzymatic Characteristics of Two κ-Carrageenases from Carrageenan-Degrading Bacterium Catenovulum agarivorans DS2

κ-Carrageenase plays an important role in achieving the high-value utilization of carrageenan. Factors such as the reaction temperature, thermal stability, catalytic efficiency, and product composition are key considerations for its large-scale application. Previous studies have shown that the C-terminal noncatalytic domains (nonCDs) could influence the enzymatic properties, of κ-carrageenases, providing a strategy for exploring κ-carrageenases with different properties, especially catalytic products. Accordingly, two κ-carrageenases (CaKC16A and CaKC16B), from the Catenovulum agarivorans DS2, were selected and further characterized. Bioinformatics analysis suggested that CaKC16A contained a nonCD but CaKC16B did not. CaKC16A exhibited better enzymatic properties than CaKC16B, including thermal stability, substrate affinity, and catalytic efficiency. After truncation of the nonCD of CaKC16A, its thermal stability, substrate affinity, and catalytic efficiency have significantly decreased, indicating the vital role of nonCD in maintaining a good enzymatic property. Moreover, CaKC16A degraded κ-carrageenan to produce a highly single κ-neocarratetrose, while CaKC16B produced a single κ-neocarrabiose. CaKC16A could degrade β/κ-carrageenan to produce a highly single desulfated κ-neocarrahexaose, while CaKC16B produced κ-neocarrabiose and desulfated κ-neocarratetrose. Furthermore, it was proposed that CaKC16A and CaKC16B participate in the B/KC metabolic pathway and serve different roles, providing new insight into obtaining κ-carrageenases with different properties.

Biochemical Characterization of a Heat-Resistant κ-Carrageenase Capable of Tolerating High Temperatures up to 100 °C

κ-Carrageenase plays a crucial role in the high-value utilization of carrageenan. Heat resistance is a key factor in the practical application of κ-carrageenase, as carrageenan exhibits gel-like properties. Previous studies have shown that the C-terminal noncatalytic domains (nonCDs) can affect the thermostability of κ-carrageenases. In this study, we expressed and characterized a κ-carrageenase, MtKC16A, which contains three nonCDs, from Microbulbifer thermotolerans. MtKC16A has the highest activity at 80 °C and pH 7.0. Surprisingly, it exhibits excellent heat resistance, with 71.58% relative activity at 100 °C and still retains over 50% residual activity after incubation at 100 °C for 60 min. Additionally, MtKC16A has been shown to have a dual substrate hydrolysis activity. It can degrade κ-carrageenan to produce highly single Nκ4 and degrade β/κ-carrageenan to produce Nκ2 and desulfated Nκ4 DA-G-DA-G4S, suggesting its potential in producing κ- and β/κ-hybrid oligosaccharides. Furthermore, we found that the unknown function domain (UNFD) in MtKC16A plays the most vital role among the three nonCDs. When this UNFD is truncated, the resulting mutants completely lose their catalytic ability at 100 °C. Finally, by introducing this UNFD to the C-terminal of another κ-carrageenase CaKC16B, we were able to improve its heat resistance at 100 °C.