Comparison of Biochemical Characteristics, Action Models, and Enzymatic Mechanisms of a Novel Exolytic and Two Endolytic Lyases with Mannuronate Preference

Recent explorations of tool-like alginate lyases have been focused on their oligosaccharide-yielding properties and corresponding mechanisms, whereas most were reported as endo-type with α-L-guluronate (G) preference. Less is known about the β-D-mannuronate (M) preference, whose commercial production and enzyme application is limited. In this study, we elucidated Aly6 of Flammeovirga sp. strain MY04 as a novel M-preferred exolytic bifunctional lyase and compared it with AlgLs of Pseudomonas aeruginosa (Pae-AlgL) and Azotobacter vinelandii (Avi-AlgL), two typical M-specific endolytic lyases. This study demonstrated that the AlgL and heparinase_II_III modules play indispensable roles in determining the characteristics of the recombinant exo-type enzyme rAly6, which is preferred to degrade M-enriched substrates by continuously cleaving various monosaccharide units from the nonreducing end, thus yielding various size-defined ΔG-terminated oligosaccharides as intermediate products. By contrast, the endolytic enzymes Pae-rAlgL and Avi-rAlgL varied their action modes specifically against M-enriched substrates and finally degraded associated substrate chains into various size-defined oligosaccharides with a succession rule, changing from ΔM to ΔG-terminus when the product size increased. Furthermore, site-directed mutations and further protein structure tests indicated that H195NHSTW is an active, half-conserved, and essential enzyme motif. This study provided new insights into M-preferring lyases for novel resource discoveries, oligosaccharide preparations, and sequence determinations.

Structure Characteristics, Biochemical Properties, and Pharmaceutical Applications of Alginate Lyases

Alginate, the most abundant polysaccharides of brown algae, consists of various proportions of uronic acid epimers α-L-guluronic acid (G) and β-D-mannuronic acid (M). Alginate oligosaccharides (AOs), the degradation products of alginates, exhibit excellent bioactivities and a great potential for broad applications in pharmaceutical fields. Alginate lyases can degrade alginate to functional AOs with unsaturated bonds or monosaccharides, which can facilitate the biorefinery of brown algae. On account of the increasing applications of AOs and biorefinery of brown algae, there is a scientific need to explore the important aspects of alginate lyase, such as catalytic mechanism, structure, and property. This review covers fundamental aspects and recent developments in basic information, structural characteristics, the structure–substrate specificity or catalytic efficiency relationship, property, molecular modification, and applications. To meet the needs of biorefinery systems of a broad array of biochemical products, alginate lyases with special properties, such as salt-activated, wide pH adaptation range, and cold adaptation are outlined. Withal, various challenges in alginate lyase research are traced out, and future directions, specifically on the molecular biology part of alginate lyases, are delineated to further widen the horizon of these exceptional alginate lyases.

Efficient Degradation of Alginate And Preparation of Unsaturated Monosaccharides By A Novel Alginate Lyase And Effects of Domain Truncation On Biochemical Characteristics, Degradation Patterns

BackgroundBrown algae are considered promising crops for the production of sustainable biofuels. However, its commercial application has been limited by lack of efficient methods for converting alginate into fermentable sugars. Recently, exo-type alginate lyases have received extensive attention due to their excellent ability of conversion of alginate into 4-deoxy-L-erythro-5-hexoseulose uronate (DEH), a promising material for bioethanol production and biorefinery systems.ResultsHerein, we cloned and characterized a novel alginate lyase AlyPL17 from Pedobacter hainanensis NJ-02. It possessed outstanding catalytic efficiency towards polymannuronic acid (polyM), polyguluronic acid (polyG) and alginate sodium, with kcat of 39.42 + 1.9 s-1, 32.53 + 0.88 s-1, and 38.30 + 2.12 s-1, respectively. In addition, AlyPL17 adopts a unique hybrid action mode to degrade alginate by the synergistic effect of two domains. Furthermore, the combination of AlyPL17 and AlyPL6 exhibited apparently synergistic effect for the preparation of unsaturated monosaccharides. ConclusionOverall, the results show that AlyPL17 is a PL17 exo-type alginate lyase with high activity and a high conversion rate at low/moderate temperatures, which provides a useful enzymatic tool for the conversion of brown algae into biofuels and enhance our understanding of the function of modular domain of alginate lyase.

Bacterial alginate metabolism: an important pathway for bioconversion of brown algae

Brown macroalgae have attracted great attention as an alternative feedstock for biorefining. Although direct conversion of ethanol from alginates (major components of brown macroalgae cell walls) is not amenable for industrial production, significant progress has been made not only on enzymes involved in alginate degradation, but also on metabolic pathways for biorefining at the laboratory level. In this article, we summarise recent advances on four aspects: alginate, alginate lyases, different alginate-degrading systems, and application of alginate lyases and associated pathways. This knowledge will likely inspire sustainable solutions for further application of both alginate lyases and their associated pathways.

Comparison of the Values of a Novel Exolytic and Two Endolytic Alginate Lyases with Mannuronate Preference for Direct Preparation of Oligosaccharides, Action Modes, and Underlying Catalytic Mechanisms

Recent exploration of tool-like alginate lyases has focused on their oligosaccharide products and corresponding substrate action modes, and most were characterized as endolytic lyases with guluronate (G) preference. Herein, we elucidated a novel exolytic lyase, Aly-6, and two typical endolytic lyases, AlgL-Pae and AlgL-Avi, all with mannuronate (M) preferences. AlgL and heparinase_II_III modules play essential roles in determining the similar characteristics of these enzymes, although they are quite different in sequence characteristics. Aly-6 degraded substrates completely by continuously cleaving various monosaccharide units from nonreducing ends and producing various size-defined ΔG-terminated oligosaccharide fractions as intermediate alginate digests, which was inhibited by fluorescent labeling of reducing ends. Distinctly, AlgL-Pae and AlgL-Avi varied their action modes toward associated alginate substrates and therefore eventually degraded alginate into various size-defined oligosaccharide products with a specific structure-based succession rule. This study provided new insights into the action modes, associated mechanisms, and enzyme applications of M-preferred lyases.

Degradation and utilization of Alginate by marine Pseudoalteromonas : a review

Alginate, which is mainly produced by brown algae and decomposed by heterotrophic bacteria, is an important marine organic carbon source. The genus Pseudoalteromonas contains diverse forms of heterotrophic bacteria that are widely distributed in marine environments and are an important group in alginate degradation. In this review, the diversity of alginate-degrading Pseudoalteromonas is introduced and the character of Pseudoalteromonas alginate lyases, including their sequences, enzymatic properties, structures and catalytic mechanisms, and the synergistic effect of Pseudoalteromonas alginate lyases on alginate degradation are introduced. The acquisition of the alginate-degradation capacity and the alginate utilization pathways of Pseudoalteromonas are also introduced. This paper provides a comprehensive overview of alginate degradation by Pseudoalteromonas, which will contribute to the understanding of the degradation and recycling of marine algae polysaccharides driven by marine bacteria.