Characterization of a family 3 polysaccharide lyase with broad temperature adaptability, thermo-alkali stability, and ethanol tolerance

The 774-bp pectate lyase gene plyAI4 from Bacillus sp. I4 was cloned and expressed in E. coli. The gene encodes a 257-residue polypeptide (PlyAI4, 28.3 kDa) with the highest identities of 97.3% with a putative pectate lyase from Bacillus subtilis BSn5 (ADV94306) and 60.3% with an identified pectate lyase of the polysaccharide lyase family (PL) 3 from Paenibacillus amylolyticus 27C64 (ADB78774). The purified recombinant PlyAI4 (rPlyAI4) exhibited apparently optimal activity at pH 10.5~11.0 and 50℃. Compared with the majority of reported alkaline pectate lyases, rPlyAI4 exhibited more residual enzyme activity at 20℃ (~45%) or at 70℃ (~50%) and better thermostability at 70℃ (~60 min half-life at 70℃). In the presence of 20% (v/v) ethanol, pectate lyase activity was enhanced by 0.2 fold. After incubation in 40% (v/v) ethanol at 37℃ and pH 8.5 for 1 h, the purified rPelAI4 retained more than 75% of the initial activity. Sequence analysis proposed a new signature block, A-D-G-[V/I]-H, for PL 3 pectate lyases. These properties may prove to be important with regards to PlyAI4 for basic research and industrial application.