Elucidation of degrading pattern and substrate recognition of a novel bifunctional alginate lyase from Flammeovirga sp. NJ-04 and its use for preparation alginate oligosaccharides

Benwei Zhu,Zhong Yao,Fang Ni,Limin Ning,Yun Sun

doi:10.1186/s13068-019-1352-8

Abstract

BackgroundThe alginate oligosaccharides have been widely used in agriculture, medicine, and food industries due to their versatile physiological functions such as antioxidant, anticoagulant, and antineoplastic activities. The bifunctional alginate lyases can degrade the alginate polysaccharide more efficiently into alginate oligosaccharides. Therefore, it is crucial to discover new bifunctional alginate lyase for alginate oligosaccharide production.ResultsHerein, a novel bifunctional alginate lyase FsAlgB was cloned and identified from deep-sea bacterium Flammeovirga sp. NJ-04, which exhibited broad substrate specificity and the highest activity (1760.8 U/mg) at pH 8.0 and 40 °C. Furthermore, the Km values of FsAlgB towards polyG (0.69 mM) and polyMG (0.92 mM) were lower than that towards sodium alginate (1.28 mM) and polyM (2.06 mM). Recombinant FsAlgB was further characterized as an endolytic alginate lyase, and it can recognize the tetrasaccharide as the minimal substrate and cleave the glycosidic bonds between the subsites of − 3 and + 1.ConclusionThis study provided extended insights into the substrate recognition and degrading pattern of alginate lyases with broad substrate specificity.

Highlights

The alginate oligosaccharides have been widely used in agriculture, medicine, and food industries due to their versatile physiological functions such as antioxidant, anticoagulant, and antineoplastic activities
As shown in Additional file 1: Figure S1, the open reading frame (ORF) of FsAlgB consists of 900 bp and encodes a putative alginate lyase composed of 299 amino acids with a theoretical molecular mass of 34.50 kDa
In this study, a novel bifunctional alginate lyase FsAlgB has been identified from Flammeovirga sp

Summary

Introduction

The alginate oligosaccharides have been widely used in agriculture, medicine, and food industries due to their versatile physiological functions such as antioxidant, anticoagulant, and antineoplastic activities. The bifunctional alginate lyases can degrade the alginate polysaccharide more efficiently into alginate oligosaccharides. It is crucial to discover new bifunctional alginate lyase for alginate oligosaccharide production. Alginate is the main component of the cell wall of brown algae such as Laminaria japonica [1]. It is a linear acidic polysaccharide consisting of β-d-mannuronate (M) and its C5 epimer α-l-guluronate (G). Alginate lyase and can degrade alginate into unsaturated oligosaccharides by β-elimination [7]. Endolytic enzymes can recognize and cleave glycosidic bonds inside alginate polymers with unsaturated oligosaccharides (such as di-, tri-, and tetra-saccharides) as main products [10], while exolytic ones can further degrade oligosaccharides into monomers [11]. According to protein sequence similarity, alginate lyases are organized into the PL-5, 6, 7, 14, 15, 17, and 18 families (http://www.cazy. org/fam/acc_PL.html) [12]

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Discussion

Conclusion