Crystal structure of PfbA, a surface adhesin of Streptococcus pneumoniae, provides hints into its interaction with fibronectin

PfbA is a surface adhesin and invasin of Streptococcus pneumoniae that binds to human fibronectin and plasminogen of the host extracellular matrix. It is a virulence factor for its pathogenesis. The crystal structure of recombinant PfbA(150-607) from S. pneumoniae strain R6, was determined using multiwave-length anomalous dispersion (MAD) method and refined to 1.90 angstrom resolution. The structure of rPfbA(150-607) revealed that residues Thr150 to Lys570 form a rigid parallel beta helix, followed by a short disordered region (571-607) that consists of beta hairpins. The structural organization of the beta helix resembles that of polysaccharide-modifying enzymes. The structural and sequence features essential for fibronectin-binding observed in the well characterized fibronectin-binding proteins such as FnBPA of Staphylococcus aureus, SfbI of Streptococcus pyogenes and BBK32 of Borrelia burgdorferi has been found in rPfbA(150-607). Based on this, it is predicted that the disordered region following the beta helix could be the fibronectin-binding region in PfbA. PfbA(150-607) contains relatively high number of surface exposed lysines and these residues are probably involved in binding plasmin(ogen) as observed in other plasminogen-binding proteins. (C) 2013 Elsevier B.V. All rights reserved.