Heterologous Expression and Characterization of Cellouronate (β-1,4-Glucuronan) Lyase from a Human Intestinal Bacterium .

Cellouronate, β-1,4-glucuronan, is synthesized from regenerated cellulose via 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radical-mediated oxidation. Human intestinal bacteria were cultured in a medium containing cellouronate to evaluate its utilization. These experiments showed to grow well in this medium. Several putative cellouronate lyases belonging to polysaccharide lyase family 38 from were identified. Among these candidate enzymes, CUL1, which displayed the most similarity to authentic cellouronate lyases, was heterologously expressed and characterized. The recombinant CUL1 (rCUL1) showed the highest activity at pH 8.0 and was deactivated by treatment at pH 3.0 for 24 h or heating above 50 °C for 10 min. Moreover, the activity of rCUL1 was enhanced in the presence of Mg, Ca, or EDTA, but suppressed by Al and completely inactivated by Fe. Analysis of the final reaction mixture generated from the rCUL1 mediated degradation of cellouronate revealed an oligomer as the main product, but the monomer was barely detectable. This study is the first to report and characterize a cellouronate lyase from human intestinal bacteria.