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.