Agarases are the enzymes which catalyze the hydrolysis of agar. They are classified into α-agarase (E.C. 3.2.1.158) and β-agarase (E.C. 3.2.1.81) according to the cleavage pattern. Several agarases have been isolated from different genera of bacteria found in seawater and marine sediments, as well as engineered microorganisms. Agarases have wide applications in food industry, cosmetics, and medical fields because they produce oligosaccharides with remarkable activities. They are also used as a tool enzyme for biological, physiological, and cytological studies. The paper reviews the category, source, purification method, major characteristics, and application fields of these native and gene cloned agarases in the past, present, and future.

https://www.mdpi.com/1660-3397/8/1/200/pdf

Agarase: review of major sources, categories, purification method, enzyme characteristics and applications.

Red algae (Rhodophyta) are known as the source of unique sulfated galactans, such as agar, agarose, and carrageenans. The wide practical uses of these polysaccharides are based on their ability to form strong gels in aqueous solutions. Gelling polysaccharides usually have molecules built up of repeating disaccharide units with a regular distribution of sulfate groups, but most of the red algal species contain more complex galactans devoid of gelling ability because of various deviations from the regular structure. Moreover, several red algae may contain sulfated mannans or neutral xylans instead of sulfated galactans as the main structural polysaccharides. This chapter is devoted to a description of the structural diversity of polysaccharides found in the red algae, with special emphasis on the methods of structural analysis of sulfated galactans. In addition to the structural information, some data on the possible use of red algal polysaccharides as biologically active polymers or as taxonomic markers are briefly discussed.

Polysaccharides of the red algae.

Agar is a mixture of heterogeneous galactans, mainly composed of 3,6-anhydro-l-galactoses (or l-galactose-6-sulfates) d-galactoses and l-galactoses (routinely in the forms of 3,6-anhydro-l-galactoses or l-galactose-6-sulfates) alternately linked by β-(1,4) and α-(1,3) linkages. It is a major component of the cell walls of red algae and has been used in a variety of laboratory and industrial applications, owing to its jellifying properties. Many microorganisms that can hydrolyze and metabolize agar as a carbon and energy source have been identified in seawater and marine sediments. Agarolytic microorganisms commonly produce agarases, which catalyze the hydrolysis of agar. Numerous agarases have been identified in microorganisms of various genera. They are classified according to their cleavage pattern into three types—α-agarase, β-agarase, and β-porphyranase. Although, in a broad sense, many other agarases are involved in complete hydrolysis of agar, most of those identified are β-agarases. In this article we review agarolytic microorganisms and their agar-hydrolyzing systems, covering β-agarases as well as α-agarases, α-neoagarobiose hydrolases, and β-porphyranases, with emphasis on the recent discoveries. We also present an overview of the biochemical and structural characteristics of the various types of agarases. Further, we summarize and compare the agar-hydrolyzing systems of two specific microorganisms: Gram-negative Saccharophagus degradans 2–40 and Gram-positive Streptomyces coelicolor A3(2). We conclude with a brief discussion of the importance of agarases and their possible future application in producing oligosaccharides with various nutraceutical activities and in sustainably generating stock chemicals for biorefinement and bioenergy.

Agar degradation by microorganisms and agar-degrading enzymes

β-Agarases are mostly categorized into three glycoside hydrolase (GH) families 16, 50, and 86. Recent genomic analysis of Saccharophagus degradans 2–40 revealed the presence of five agarase genes belonging to these GH families. Among the five agarases, Aga50D (a member of GH50) had neither been functionally characterized nor overexpressed. In this report, we present soluble overexpression and molecular characterization of Aga50D. Aga50D was expressed in an active form resulting in a single major product from agarose without intermediates. While known GH50 agarases have both endo-lytic and exo-lytic activities, which produce neoagarobiose as a final product through the intermediate, neoagaro-oligosaccharides, identification and analysis of the reaction product by mass spectrometry and 13C NMR showed that Aga50D had unique exo-lytic activity and was able to produce neoagarobiose directly from agarose. The optimum pH and temperature for the activity were 7.0 and 30°C, respectively. The K
 m and V
 max for agarose were 41.9 mg/ml (4.2 mM) and 17.9 U/mg, respectively.

Overexpression and molecular characterization of Aga50D from Saccharophagus degradans 2-40: an exo-type β-agarase producing neoagarobiose

Because of their potential use as functional ingredients in human nutrition, oligosaccharides derived from natural sources are receiving paramount consideration. Red seaweed, a proven rich source of agar and carrageenan, is one of the most abundantly present sources of such oligosaccharides. Agaro-oligosaccharides (AOS) and carrageenan-oligosaccharides (COS) are produced from agar and carrageenan, respectively, through chemical and enzymatic hydrolyses. Enzymatic hydrolysis of agar and carrageenan into oligosaccharides is preferred in industrial production because of certain problems associated with chemical hydrolysis, including the release of high amounts of monosaccharides and undesirable toxic products, such as furfural. AOS and COS possess many biological activities, including prebiotic, immuno-modulatory, anti-oxidant, and anti-tumor activities. These activities are related to their chemical structure, molecular weight, degree of polymerization, and the flexibility of the glycosidic linkages. Therefore, the structure⁻function relationship and the mechanisms occurring during the specific biological applications of AOS and COS are discussed herein. Moreover, the chromatographic separation, purification, and characterization of AOS and COS are also part of this review. This piece of writing strives to create a new perspective on the potential applications of AOS and COS in the functional food and pharmaceutical industry.

https://www.mdpi.com/1420-3049/23/10/2451/pdf

Oligosaccharides Derived from Red Seaweed: Production, Properties, and Potential Health and Cosmetic Applications.

Neoagarobiose, a disaccharide, showed a higher hygroscopic ability than glycerol or hyaluronic acid, typical moisturizing reagents. Beside, neoagarobiose whitened B16 murine melanoma cells, and showed low cytotoxicity. Therefore neoagarobiose was a rare reagent showing both moisturizing and whitening effects.

Mikimasa Takisada

Papers

Neoagarobiose as a novel moisturizer with whitening effect.