Characterisation of an exo-(α-1,3)-3,6-anhydro-d-galactosidase produced by the marine bacterium Zobellia galactanivorans DsijT: Insight into enzyme preference for natural carrageenan oligosaccharides and kinetic characterisation on a novel chromogenic substrate

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.

To gel or not to gel - Tuning the sulfation pattern of carrageenans to expand their field of application

Carrageenans represent a major cell wall component of red macro algae and, as established gelling and thickening agents, they contribute significantly to a broad variety of commercial applications in the food and cosmetic industry. As a highly sulfated class of linear polysaccharides, their functional properties are strongly related to the sulfation pattern of their carrabiose repeating units. Therefore, the biocatalytic fine-tuning of these polymers by generating tailored sulfation architectures harnessing the hydrolytic activity of sulfatases could be a powerful tool to produce novel polymer structures with tuned properties to expand applications of carrageenans beyond their current use. To contribute to this vision, we sought to identify novel carrageenan sulfatases by studying several putative carrageenolytic clusters in marine heterotrophic bacteria. This approach revealed two novel formylglycine-dependent sulfatases from Cellulophaga algicola DSM 14237 and Cellulophaga baltica DSM 24729 with promiscuous hydrolytic activity towards the sulfated galactose in the industrially established ι- and κ-carrageenan, converting them into α- and β-carrageenan, respectively, and enabling the production of a variety of novel pure and hybrid carrageenans. The rheological analysis of these enzymatically generated structures revealed significantly altered physicochemical properties that may open the gate to a variety of novel carrageenan-based applications.

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.

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.

Polysphaeroides filiformis, a proterozoic cyanobacterial microfossil and implications for cyanobacteria evolution

Deciphering the fossil record of cyanobacteria is crucial to understand their role in the chemical and biological evolution of the early Earth. They profoundly modified the redox conditions of early ecosystems more than 2.4 Ga ago, the age of the Great Oxidation Event (GOE), and provided the ancestor of the chloroplast by endosymbiosis, leading the diversification of photosynthetic eukaryotes. Here, we analyze the morphology, ultrastructure, chemical composition, and metals distribution of Polysphaeroides filiformis from the 1040-1006 Ma Mbuji-Mayi Supergroup (DR Congo). We evidence trilaminar and bilayered ultrastructures for the sheath and the cell wall, respectively, and the preservation of Ni-tetrapyrrole moieties derived from chlorophyll in intracellular inclusions. This approach allows an unambiguous interpretation of P. filiformis as a branched and multiseriate photosynthetic cyanobacterium belonging to the family of Stigonemataceae. It also provides a possible minimum age for the emergence of multiseriate true branching nitrogen-fixing and probably heterocytous cyanobacteria.

Enzymatically-derived oligo-carrageenans interact with α-Gal antibodies and Galectin-3

Carrageenans are linear sulfated galactans synthesized in the Gigartinales, Rhodophyceae species with a varied range of biological properties that are of value to the pharmaceutical and cosmetic sectors. It is unknown how the fine structure of carrageenans dictates their capacity to affect molecular and cellular responses important to wound healing, or the ability to mitigate oxidative, hemostatic and inflammatory processes. Here we use specific endo-carrageenases, from the marine bacterium Zobellia galactanivorans, to produce enzymatically defined neo-series oligosaccharides from carrageenans with 3,6-anhydro-D-galactose on the non-reducing end. Further enzymatic modification of the oligosaccharides was done by treating with the 3,6-anhydro-D-galactosidases from the same bacterium which hydrolyze non-reducing end 3,6-anhydro-D-galactose moieties from neo-carrageenan oligosaccharides. Using the enzymatically produced oligosaccharides, we demonstrate binding to natural human serum antibodies and a monoclonal anti-αGal Ab (m86). The significant interactions with the Galα(1,3)Gal reactive antibodies produced by humans makes them potential potent inducers of complement-dependent reactions and attractive for therapeutic applications. We also demonstrate modulation of the galectin selectivity for the Gal-3 Carbohydrate Recognition Domain (CRD) relative to Gal-1 which has implications to targeting specific biological pathways regulated by the galectins.

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

Oligosaccharides and anhydro-sugars derived from carrageenan have great potential as functional foods and drugs showing various bioactivities, including antioxidant, anti-inflammatory, antiviral, antitumor, and cytotoxic activities. Although preparation of sulfated carrageenan oligosaccharides by chemical and enzymatic processes has been widely reported, preparation of nonsulfated β-neocarrabiose (β-NC2) and the rare sugar 3,6-anhydro-d-galactose (d-AHG) was not reported in the literature. Based on the carrageenan catabolic pathway in marine heterotrophic bacteria, an enzymatic process was designed and constructed with recombinant κ-carrageenase, GH127/GH129 α-1,3 anhydrogalactosidase, and cell-free extract from marine carrageenolytic bacteria Colwellia echini A3^T. The process consisted of three successive steps, namely, (i) depolymerization, (ii) desulfation, and (iii) monomerization, by which carrageenan oligosaccharides, β-NC2, and d-AHG were obtained from κ-carrageenan. Unlike the chemical process, enzymatic hydrolysis yields oligosaccharides with the desired degree of polymerization facilitates specific removal of sulfated groups, free of toxic byproducts, and avoids chemical modifications. The final optimized enzymatic process produced 0.52 g of β-NC2 and 0.24 g of d-AHG from 1 g of κ-carrageenan. The carrageenolytic process designed for the enzymatic hydrolysis of κ-carrageenan can be scaled up for the mass production of bioactive carrageeno-oligosaccharides.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2019-2020

This review is the tenth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2020. Also included are papers that describe methods appropriate to analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. The review is basically divided into three sections: (1) general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation, quantification and the use of arrays. (2) Applications to various structural types such as oligo- and polysaccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals, and (3) other areas such as medicine, industrial processes and glycan synthesis where MALDI is extensively used. Much of the material relating to applications is presented in tabular form. The reported work shows increasing use of incorporation of new techniques such as ion mobility and the enormous impact that MALDI imaging is having. MALDI, although invented nearly 40 years ago is still an ideal technique for carbohydrate analysis and advancements in the technique and range of applications show little sign of diminishing.

Red Algal Molecules - Synthesis of Methyl Neo-β-carrabioside and Its S-Linked Variant via Two Synthetic Routes: A Late Stage Ring Closure and Using a 3,6-Anhydro-d-galactosyl Donor

Methyl neo-β-carrabioside has been synthesized for the first time, employing either a late stage ring closure to install the required 3,6-anhydro-bridge or a suitable 3,6-anhydro-galactosyl donor to form the unfavored 1,2-cis-equatorial α-linkage. Using the late stage ring closure approach, an S-linked analogue of methyl neo-β-carrabioside was also realized. These compounds have applications in the identification and characterization of marine bacterial exo-α-3,6-anhydro-d-galactosidases that have specific activity on red algal neo-carrageenan oligosaccharides, such as those found in both family 127 and 129 of the glycoside hydrolases. In addition a biochemical assay using the synthesized methyl neo-β-carrabioside and the marine bacterial exo-α-3,6-anhydro-d-galactosidase ZgGH129 demonstrates that the minimum substrate unit for the enzyme is neo-β-carrabiose.