Molecular Characterization of an Endo-β-1,4-Glucanase, CelAJ93, from the Recently Isolated Marine Bacterium, Cellulophaga sp. J9-3

Abstract

A novel cellulase was characterized from a newly isolated marine bacterium, strain J9-3. Phylogenetic analysis based on the 16S rRNA gene revealed that strain J9-3 belonged to the genus Cellulophaga, and thus, it was named Cellulophaga sp. J9-3. An extracellular cellulase was purified from cell-free culture broth of J9-3 cultured in Marine Broth containing 0.2% carboxymethylcellulose. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the protein revealed a single band with an apparent molecular weight (Mw) of 35 kDa. Based on the NH2-terminal amino acid sequence (N-N-T-E-Q-T-V-V-D-A-Y-G), the gene (named celAJ93) encoding the protein was identified from J9-3 genomic sequencing data. CelAJ93 was expected to be translated into a premature protein (359 amino acids) and then processed to a mature protein (307 amino acids, Mw = 34,951 Da), which is consistent with our results. CelAJ93 had high homology with many uncharacterized putative glycosyl hydrolases of the genus Cellulophaga and it was highly specific for carboxymethylcellulose and cellooligosaccharides under optimum conditions (pH 7.5, 60 °C). Co2+ completely recovered CelAJ93 activity that was severely inhibited by ethylenediaminetetraacetic acid (EDTA), indicating that CelAJ93 required Co2+ as a cofactor. Thus, CelAJ93 is a Co2+-dependent endo-β-1,4-glucanase that can hydrolyze carboxymethylcellulose and cellooligosaccharides into cellobiose at a relatively high temperature.