Catalytic NodB homology domain of Streptococcus pneumoniae peptidoglycan deacetylase PgdA, Bacillus subtilis BsYjeA protein, and their bacterial homologs
This family is represented by Streptococcus pneumoniae peptidoglycan GlcNAc deacetylase (SpPgdA), a member of the carbohydrate esterase 4 (CE4) superfamily. SpPgdA protects gram-positive bacterial cell wall from host lysozymes by deacetylating peptidoglycan N-acetylglucosamine (GlcNAc) residues. It consists of three separate domains: N-terminal, middle and C-terminal (catalytic) domains. The catalytic NodB homology domain is similar to the deformed (beta/alpha)8 barrel fold adopted by other CE4 esterases, which harbors a mononuclear metalloenzyme employing a conserved His-His-Asp zinc-binding triad closely associated with conserved catalytic base (aspartic acid) and acid (histidine) to carry out acid/base catalysis. The enzyme is able to accept GlcNAc3 as a substrate, with the N-acetyl of the middle sugar being removed by the enzyme. This family also includes Bacillus subtilis BsYjeA protein encoded by the yjeA gene, which is one of the six polysaccharide deacetylase gene homologs (pdaA, pdaB/ybaN, yheN, yjeA, yxkH and ylxY) in the Bacillus subtilis genome. Although homology comparison shows that the BsYjeA protein contains a polysaccharide deacetylase domain, and was predicted to be a membrane-bound xylanase or a membrane-bound chitooligosaccharide deacetylase, more recent research indicates BsYjeA might be a novel non-specific secretory endonuclease which creates random nicks progressively on the two strands of dsDNA, resulting in highly distinguishable intermediates/products very different in chemical and physical compositions over time. In addition, BsYjeA shares several enzymatic properties with the well-understood DNase I endonuclease. Both enzymes are active on ssDNA and dsDNA, both generate random nicks, and both require Mg2+ or Mn2+ for hydrolytic activity.
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