Structural highlights
Publication Abstract from PubMedCell walls of brown algae are complex supramolecular assemblies containing various original, sulfated and carboxylated polysaccharides. Among these, the major marine polysaccharide component, alginate, represents an important biomass that is successfully turned over by heterotrophic marine bacteria. In the marine flavobacterium Zobellia galactanivorans the catabolism and uptake of alginate is encoded by operon structures that resemble the typical Bacteroidetes polysaccharide utilization locus (PUL). The genome of Z. galactanivorans contains seven putative alginate lyase genes, five of which are localized within two clusters comprising additional carbohydrate-related genes. This study reports the detailed biochemical and structural characterization of two of these. We demonstrate here that AlyA1PL7 is an endolytic guluronate lyase, while AlyA5 cleaves unsaturated units, a-L-guluronate (G) or b-D-manuronate (M) residues at the non-reducing end of oligo-alginates in an exolytic fashion. Despite a common jelly-roll fold, these striking differences of mode of action are explained by a distinct active site topology: an open cleft in AlyA1PL7, whereas AlyA5 displays a pocket topology due to the presence of additional loops partially obstructing the catalytic groove. Finally, in contrast to PL7 alginate lyases from terrestrial bacteria, both enzymes proceed according a calcium-dependent mechanism suggesting an exquisite adaptation to their natural substrate in the context of brown algal cell walls. Comparative characterization of two marine alginate lyases from Zobellia galactanivorans reveals distinct modes of action and exquisite adaptation to their natural substrate.,Thomas F, Lundqvist LC, Jam M, Jeudy A, Barbeyron T, Sandstrom C, Michel G, Czjzek M J Biol Chem. 2013 Jun 19. PMID:23782694[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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