Abstract
Alginate is a polysaccharide produced by certain seaweeds and bacteria that consists of mannuronic acid and guluronic acid residues. Seaweed alginate is used in food and industrial chemical processes, while the biosynthesis of bacterial alginate is associated with pathogenic Pseudomonas aeruginosa. Alginate lyases cleave this polysaccharide into short oligo-uronates and thus have the potential to be utilized for both industrial and medicinal applications. An alginate lyase gene, algMsp, from Microbulbifer sp. 6532A, was synthesized as an E.coli codon-optimized clone. The resulting 37 kDa recombinant protein, AlgMsp, was expressed, purified and characterized. The alginate lyase displayed highest activity at pH 8 and 0.2 M NaCl. Activity of the alginate lyase was greatest at 50°C; however the enzyme was not stable over time when incubated at 50°C. The alginate lyase was still highly active at 25°C and displayed little or no loss of activity after 24 hours at 25°C. The activity of AlgMsp was not dependent on the presence of divalent cations. Comparing activity of the lyase against polymannuronic acid and polyguluronic acid substrates showed a higher turnover rate for polymannuronic acid. However, AlgMSP exhibited greater catalytic efficiency with the polyguluronic acid substrate. Prolonged AlgMsp-mediated degradation of alginate produced dimer, trimer, tetramer, and pentamer oligo-uronates.
Highlights
Alginate is a linear polysaccharide composed of two different uronic acids,b-D-mannuronic acid (M) and a-L-guluronic acid (G)
These two uronic acids are present in alginate as polymannuronic acid blocks, polyguluronic acid blocks and in mixed MG regions
AlgMsp belongs to the alginate lyase 2 family, pfam08787, of the Conserved Domains database [30]
Summary
Alginate is a linear polysaccharide composed of two different uronic acids,b-D-mannuronic acid (M) and a-L-guluronic acid (G). These two uronic acids are present in alginate as polymannuronic acid blocks (polyM), polyguluronic acid blocks (polyG) and in mixed MG regions. Alginate lyases are enzymes that degrade alginate by a belimination reaction that breaks the 1–4 O-linkage between the uronic acids in the linear polymer. This reaction results in the formation of a double bond between carbons 4 and 5 of the uronic acid that was linked at the 4th carbon. Alginate lyases can have substrate preferences for polyM or polyG present in the alginate
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