Background: Alginate lyases belonging to polysaccharide lyase family-7 (PL-7) are the most well studied on their structures and functions among whole alginate lyases. However, all characterized PL-7 alginate lyases are from prokaryotic bacteria cells. Here we report the first identification of eukaryotic PL-7 alginate lyase from marine red alga Pyropia yezoensis.Methods: The cDNA encoding an alginate lyase PyAly was cloned and was used for the construction of recombinant PyAly (rPyAly) expression system in Escherichia coli. Purified rPyAly was assayed to identify its enzymatic properties. Its expression pattern in P. yessoensis was also investigated.Results: PyAly is likely a secreted protein consisting of an N-terminal signal peptide of 25 residues and a catalytic domain of 216 residues. The amino-acid sequence of the catalytic domain showed 19-29% identities to those of bacterial characterized alginate lyases classified into family PL-7. Recombinant PyAly protein, rPyAly, which was produced with E. coli BL21(DE3) by cold-inducible expression system, drastically decreased the viscosity of alginate solution in the early stage of reaction. The most preferable substrate for rPyAly was the poly(M) of alginate with an optimal temperature and pH at 35oC and 8.0, respectively. After reaction, unsaturated tri- and tetra-saccharides were produced from poly(M) as major end products. These enzymatic properties indicated that PyAly is an endolytic alginate lyase belonging to PL-7. Moreover, we found that the PyAly gene is split into 4 exons with 3 introns. PyAly was also specifically expressed in the gametophytic haplopid stage.Conclusion: This study demonstrates that PyAly in marine red alga P. yezoensis is a novel PL-7 alginate lyase with an endolytic manner. PyAly is a gametophyte-specifically expressed protein and its structural gene is composed of four exons and three introns. Thus, PyAly is the first enzymatically characterized eukaryotic PL-7 alginate lyase.

Functional recombinant abalone alginate lyase (rHdAly) and β-1,4-endoglucanase (rHdEG66) were expressed as secreted proteins with baculoviral expression systems. The specific activity of each recombinant enzyme, 2,490 and 18.2 U/mg for rHdAly and rHdEG66, respectively, was comparable to its native form at 30°C. Purified rHdAly and rHdEG66 showed the highest specific activity both at 35°C and optimum pH 8.7 and 5.9, respectively. These properties were also comparable to those of the native enzymes. Protoplast isolation was attempted from Laminaria japonica using both rHdAly and rHdEG66. When L. japonica blades were incubated in artificial seawater containing rHdAly and rHdEG66, very low numbers of protoplasts (<1 × 10(3) protoplasts/g fresh weight) resulted. However, using blades pretreated with proteinase K, the protoplast was increased up to 5 × 10(6) protoplasts/g fresh weight. Since the average diameter of isolated protoplasts was 11.6 μm, these cells were mostly derived from the epidermal layer rather than the cortical layer. Our results suggest that at least three enzymes, alginate lyase, cellulase, and protease, are essential for effective protoplast isolation from L. japonica. The protoplast isolation method in this study is more useful than earlier methods because it preferentially yielded protoplasts of the epidermal layer, which are known to be able to be regenerated.