Elucidation of a specific alginate lyase Aly7Rm: The products demonstrated the strict recognition of G residue at subsites ±2

An alginate lyase Aly7Rm with novel subsite specificity was cloned, expressed and characterized in this article. Aly7Rm was a G-specific alginate lyase, exhibiting optimum reaction conditions at 30 °C and pH 5.0. UPSEC-VWD-MS analysis revealed that Aly7Rm degraded polysaccharides in a random endo-acting manner. The main degradation products of alginate were trisaccharide to octasaccharide and those of PG were disaccharide to hexasaccharide. The product distribution was related to the specificity of enzyme and the structure of substrates. By utilizing the HPAEC-PAD/MS method, the structure of products was identified and the specificities of subsite were defined. Aly7Rm accommodated both G and M at subsites −1 and strictly recognized G at subsite −2 and +2. This is the first report on the alginate lyase exhibiting G specificity at subsites ±2, which shed light on the diversity in subsite specificity of alginate lyases. The Aly7Rm with clear action pattern could serve as an efficient tool in the specific degradation of alginate and targeted preparation of oligosaccharides.