Enzymatic Process for the Carrageenolytic Bioconversion of Sulfated Polygalactans into β-Neocarrabiose and 3,6-Anhydro-d-galactose

Structure, function and catalytic mechanism of the carrageenan-sulfatases from the marine bacterium Zobellia galactanivorans DsijT

Carrageenans are highly diverse sulfated galactans found in red seaweeds. They play various physiological roles within macroalgae, but also serve as carbon sources for heterotrophic marine bacteria living at their surface. Carrageenan sulfatases catalyze the removal of sulfate esters from the glycans to expose the saccharide chain for further enzymatic processing. In the marine flavobacterium Zobellia galactanivorans, three carrageenan sulfatase genes are localized within a carrageenan utilization locus, belonging to three distinct SulfAtlas S1 (formylglycine-dependent sulfatases) subfamilies (S1_19, ZgCgsA; S1_7, ZgCgsB1; and S1_17, ZgCgsC). In this study we combined several techniques to characterize the detailed desulfurylation steps in the catabolic pathway of carrageenan in this model marine bacterium. High resolution UHPLC-MS/MS sequencing of the reaction species provides precise chemical localization of the enzymatic activities for the three carrageenan sulfatases on carrageenan polysaccharides and oligosaccharides. High resolution structures of the S1_19 endo-/exo-lytic carrageenan sulfatase (ZgCgsA) in complex with oligocarrageenan products show substrate plasticity which involve enzyme and glycan conformational rearrangements. A sulfo-enzyme covalent-intermediate sheds light on the catalytic mechanism and highlights the unique chemistry of formylglycine, an essential post-translationally modified catalytic residue in the active site of S1 family sulfatases.

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.

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.

Chemically modified seaweed polysaccharides: Improved functional and biological properties and prospective in food applications

Seaweed polysaccharides are natural biomacromolecules with unique physicochemical properties (e.g., good gelling, emulsifying, and film-forming properties) and diverse biological activities (e.g., anticoagulant, antioxidant, immunoregulatory, and antitumor effects). Furthermore, they are nontoxic, biocompatible and biodegradable, and abundant in resources. Therefore, they have been widely utilized in food, cosmetics, and pharmaceutical industries. However, their properties and bioactivities sometimes are not satisfactory for some purposes. Modification of polysaccharides can impart the amphiphilicity and new functions to the biopolymers and change the structure and conformation, thus effectively improving their functional properties and biological activities so as to meet the requirement for targeted applications. This review outlined the modification methods of representative red algae polysaccharides (carrageenan and agar), brown algae polysaccharides (fucoidan, alginate, and laminaran), and green algae polysaccharides (ulvan) that have potential food applications, including etherification, esterification, degradation, sulfation, phosphorylation, selenylation, and so on. The improved functional properties and bioactivities of the modified seaweed polysaccharides and their potential food applications are also summarized.

Biocatalytic Conversion of Carrageenans for the Production of 3,6-Anhydro-D-galactose

Marine biomass stands out as a sustainable resource for generating value-added chemicals. In particular, anhydrosugars derived from carrageenans exhibit a variety of biological functions, rendering them highly promising for utilization and cascading in food, cosmetic, and biotechnological applications. However, the limitation of available sulfatases to break down the complex sulfation patterns of carrageenans poses a significant limitation for the sustainable production of valuable bioproducts from red algae. In this study, we screened several carrageenolytic polysaccharide utilization loci for novel sulfatase activities to assist the efficient conversion of a variety of sulfated galactans into the target product 3,6-anhydro-D-galactose. Inspired by the carrageenolytic pathways in marine heterotrophic bacteria, we systematically combined these novel sulfatases with other carrageenolytic enzymes, facilitating the development of the first enzymatic one-pot biotransformation of ι- and κ-carrageenan to 3,6-anhdyro-D-galactose. We further showed the applicability of this enzymatic bioconversion to a broad series of hybrid carrageenans, rendering this process a promising and sustainable approach for the production of value-added biomolecules from red-algal feedstocks.