Biochemical and structural characterization of the complex agarolytic enzyme system from the marine bacterium Zobellia galactanivorans.

ABSTRACT: Zobellia galactanivorans is an emerging model bacterium for the bioconversion of algal biomass. Notably, this marine Bacteroidetes possesses a complex agarolytic system comprising four ?-agarases and five ?-porphyranases, all belonging to the glycoside hydrolase family 16. Although ?-agarases are specific for the neutral agarobiose moieties, the recently discovered ?-porphyranases degrade the sulfated polymers found in various quantities in natural agars. Here, we report the biochemical and structural comparison of five ?-porphyranases and ?-agarases from Z. galactanivorans. The respective degradation patterns of two ?-porphyranases and three ?-agarases are analyzed by their action on defined hybrid oligosaccharides. In light of the high resolution crystal structures, the biochemical results allowed a detailed mapping of substrate specificities along the active site groove of the enzymes. Although PorA displays a strict requirement for C6-sulfate in the -2- and +1-binding subsites, PorB tolerates the presence of 3-6-anhydro-l-galactose in subsite -2. Both enzymes do not accept methylation of the galactose unit in the -1 subsite. The ?-agarase AgaD requires at least four consecutive agarose units (DP8) and is highly intolerant to modifications, whereas for AgaB oligosaccharides containing C6-sulfate groups at the -4, +1, and +3 positions are still degraded. Together with a transcriptional analysis of the expression of these enzymes, the structural and biochemical results allow proposition of a model scheme for the agarolytic system of Z. galactanivorans.

SUBMITTER: Hehemann JH 

PROVIDER: S-EPMC3436304 | biostudies-literature | 2012 Aug

REPOSITORIES: biostudies-literature