Abstract
Enzymatic preparation of alginate oligosaccharides with versatile bioactivities by alginate lyases has attracted increasing attention due to its featured characteristics, such as wild condition and specific products. In this study, AlgNJ-07, a novel polyM-specific alginate lyase with high specific activity and pH stability, has been purified from the newly isolated marine bacterium Serratia marcescens NJ-07. It has a molecular weight of approximately 25 kDa and exhibits the maximal activity of 2742.5 U/mg towards sodium alginate under 40 °C at pH 9.0. Additionally, AlgNJ-07 could retain more than 95% of its activity at pH range of 8.0–10.0, indicating it possesses excellent pH-stability. Moreover, it shows high activity and affinity towards polyM block and no activity to polyG block, which suggests that it is a strict polyM-specific alginate lyase. The degradation pattern of AlgNJ-07 has also been explored. The activity of AlgNJ-07 could be activated by NaCl with a low concentration (100–300 mM). It can be observed that AlgNJ-07 can recognize the trisaccharide as the minimal substrate and hydrolyze the trisaccharide into monosaccharide and disaccharide. The TLC and ESI-MS analysis indicate that it can hydrolyze substrates in a unique endolytic manner, producing not only oligosaccharides with Dp of 2–5 but also a large fraction of monosaccharide. Therefore, it may be a potent tool to produce alginate oligosaccharides with lower Dps (degree of polymerization).
Highlights
Alginate is the major component of cell wall of brown algae [1]
According to the phylogenetic analysis of 16S rRNA sequence (Figure 1), the strain was assigned to the genus Serratia and named Serratia marcescens NJ-07
The results showed that AlgNJ-07 had a much lower Km values towards polyM than sodium alginate, indicating that it showed higher affinity towards polyM than that to sodium alginate
Summary
Alginate is the major component of cell wall of brown algae [1] It is a linear anionic polysaccharide and consists of α-L-guluronate (G) and its C5 epimer β-D-mannuronate (M), which are linked by α-1, 4-glycosidic bonds [2]. Many alginate lyases originating from marine microorganisms have been well characterized Few of these enzymes have been commercially used in the food and nutraceutical industries due to the poor substrate specificity and low activity [30,31,32,33,34,35,36]. To evaluate the enzyme for potential use in the food and nutraceutical industries, the kinetics and analysis of degrading products has been characterized, which suggests that it would be a potential candidate for expanding applications of alginate lyases
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