In silico analysis of a family of extracellular polysaccharide deacetylases involved in virulence of pathogenic gram-positive cocci
© Aziz; licensee BioMed Central Ltd. 2010
Published: 23 July 2010
Pathogenic bacteria incessantly evolve mechanisms to resist their host’s innate immunity. One such mechanism is molecular camouflage: the modification of bacterial surface molecules to make them unrecognizable by the host’s immune system or resistant to its effector molecules. Recently, a peptidoglycan deacetylase (PgdA) was discovered in Streptococcus pneumoniae that renders bacterial peptidoglycan resistant to human lysozyme, thus preventing host-mediated cell wall damage[1–3]. In addition, polysaccharide deacetylases with different substrate specificities were identified in other gram-positive bacteria and shown to contribute to virulence (e.g., IcaB of Staphylococcus epidermidis  and Pdi or Streptococcus iniae ).
Materials and methods
In this study, genomes of streptococci and other representative gram-positive cocci were screened for the presence of functional homologs of PgdA, the prototypic pneumococcal peptidoglycan deacetylase. Subsequently, amino acid sequences of homologous proteins were aligned and mapped to the three-dimensional structure of PgdA (Protein Data Bank ID: 2c1g). The ConSurf tool[7, 8] was used for surface mapping of the phylogenetic information calculated from the multiple sequence alignments.
Taken together, these data suggest the conservation of PgdA in pathogenic streptococci, the presence of PgdA orthologs and paralogs in gram-positive cocci, and the high conservation of amino acid residues surrounding the active site of these enzymes. These residues may be tested as potential targets for the rational design of novel, immune-assisted antibacterial agents.
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