The endo-β-agarases AgaA and AgaB from the marine bacterium Zobellia galactanivorans: two paralogue enzymes with different molecular organizations and catalytic behaviours

摘要: Two β-agarase genes, agaA and agaB, were functionally cloned from the marine bacterium Zobellia galactanivorans. The agaB genes encode proteins of 539 353 amino acids respectively, with theoretical masses 60 40 kDa. These two β-agarases feature homologous catalytic domains belonging to family GH-16. However, AgaA displays a modular architecture, consisting domain (AgaAc) C-terminal unknown function which are processed during secretion enzyme. In contrast, AgaB is composed module signal peptide similar N-terminal signature prokaryotic lipoproteins, suggesting that this protein anchored in cytoplasmic membrane. Gel filtration electrospray MS experiments demonstrate dimer solution, while AgaAc monomeric protein. overexpressed Escherichia coli purified homogeneity. Both enzymes cleave β-(1→4) linkages agarose random manner retention anomeric configuration. Although they behave similarly towards liquid agarose, more efficient than degradation gels. Given these organizational differences, we propose that, reminiscent agarolytic system Pseudoalteromonas atlantica, specialized initial attack on solid-phase involved fragments.