Abstract
Marine bacterial alginate lyases play a role in marine alginate degradation and carbon cycling. Although a large number of alginate lyases have been characterized, reports on alginate lyases with special characteristics are still rather less. Here, a gene alyPM encoding an alginate lyase of polysaccharide lyase family 7 (PL7) was cloned from marine Pseudoalteromonas sp. SM0524 and expressed in Escherichia coli. AlyPM shows 41% sequence identity to characterized alginate lyases, indicating that AlyPM is a new PL7 enzyme. The optimal pH for AlyPM activity was 8.5. AlyPM showed the highest activity at 30°C and remained 19% of the highest activity at 5°C. AlyPM was unstable at temperatures above 30°C and had a low Tm of 37°C. These data indicate that AlyPM is a cold-adapted enzyme. Moreover, AlyPM is a salt-activated enzyme. AlyPM activity in 0.5–1.2 M NaCl was sixfolds higher than that in 0 M NaCl, probably caused by a significant increase in substrate affinity, because the Km of AlyPM in 0.5 M NaCl decreased more than 20-folds than that in 0 M NaCl. AlyPM preferably degraded polymannuronate and mainly released dimers and trimers. These data indicate that AlyPM is a new PL7 endo-alginate lyase with special characteristics.
Highlights
Alginates are mainly produced by brown algae in the ocean, which are an important component of marine organic carbon
Sequence alignment of AlyPM with AlyVGI and other polysaccharide lyase family 7 (PL7) alginate lyases that have crystal structures indicates that these conserved motifs in AlyPM are RSELR (SA3), YFKAGAYNQ (SA4), and QIH (SA5) (Figure 1)
Sequence analysis showed that AlyPM belongs to the PL7 family
Summary
Alginates are mainly produced by brown algae in the ocean, which are an important component of marine organic carbon. Structural analysis shows that these lyases share a common β-sandwich fold consisting of two β-sheets, in which, conserved amino acid residues compose a deep active cleft that is covered by two flexible lid loops (Yamasaki et al, 2004, 2005; Osawa et al, 2005; Thomas et al, 2013) There are both endo-lytic and exo-lytic alginate lyases in this family. AlyPM was shown to be a salt-activated endo-enzyme, which mainly released dimers and trimers from sodium alginate and polyM These special characteristics of AlyPM indicate that AlyPM is well adapted to marine environment and may play a role in marine alginate degradation and carbon cycling
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