title: Penicillin binding protein 3 of Staphylococcus aureus NCTC 8325-4 binds and activates human plasminogen.
abstract: BACKGROUND
  Staphylococcus aureus is a versatile pathogen expressing a number of virulence-associated adhesive molecules. In a previous study, we generated in a secretion-competent Escherichia coli strain a library of random FLAG-tag positive (FTP) polypeptides of S. aureus. To identify adhesive proteins and gain additional knowledge on putative virulence factors of S. aureus, we here screened the FTP library against human serum proteins.
  
  
  RESULTS
  Staphylococcus aureus NCTC 8325-4, origin of the FTP library, adhered to immobilized plasminogen in vitro. In an enzyme-linked immunoassay a C-terminal part of penicillin binding protein 3 (PBP3), included in the FTP library, bound to immobilized plasminogen. We expressed and purified full-length PBP3 and its C-terminal fragments as recombinant proteins. In a time-resolved fluorometry-based assay the PBP3 polypeptides bound to immobilized plasminogen. The polypeptides enhanced formation of plasmin from plasminogen as analyzed by cleavage of a chromogenic plasmin substrate.
  
  
  CONCLUSIONS
  The present findings, although preliminary, demonstrate reliably that S. aureus NCTC 8325-4 adheres to immobilized plasminogen in vitro and that the adhesion may be mediated by a C-terminal fragment of the PBP3 protein. The full length PBP3 and the penicillin binding C-terminal domain of PBP3 expressed as recombinant proteins bound plasminogen and activated plasminogen to plasmin. These phenomena were inhibited by the lysine analogue ε-aminocaproic acid suggesting that the binding is mediated by lysine residues. A detailed molecular description of surface molecules enhancing the virulence of S. aureus will aid in understanding of its pathogenicity and help in design of antibacterial drugs in the future.
authors.affiliation: General Microbiology, Department of Biosciences, University of Helsinki, P.O.Box 56, FI-00014, University of Helsinki, Helsinki, Finland.|Thermo Fisher Scientific, Ratastie 2, 01620, Vantaa, Finland.
authors.forename: Riikka
authors.initials: R
authors.lastname: Kylväjä
authors.affiliation: General Microbiology, Department of Biosciences, University of Helsinki, P.O.Box 56, FI-00014, University of Helsinki, Helsinki, Finland.|Orion Diagnostica, Koivu-Mankkaan tie 6, 02200, Espoo, Finland.
authors.forename: Tuomas
authors.initials: T
authors.lastname: Ojalehto
authors.affiliation: General Microbiology, Department of Biosciences, University of Helsinki, P.O.Box 56, FI-00014, University of Helsinki, Helsinki, Finland.|Pharmacology, Faculty of Medicine, University of Helsinki, P.O.Box 63, FI-00014, University of Helsinki, Helsinki, Finland.
authors.forename: Veera
authors.initials: V
authors.lastname: Kainulainen
authors.affiliation: General Microbiology, Department of Biosciences, University of Helsinki, P.O.Box 56, FI-00014, University of Helsinki, Helsinki, Finland.
authors.forename: Ritva
authors.initials: R
authors.lastname: Virkola
authors.affiliation: General Microbiology, Department of Biosciences, University of Helsinki, P.O.Box 56, FI-00014, University of Helsinki, Helsinki, Finland. benita.westerlund@helsinki.fi.
authors.forename: Benita
authors.identifier: http://orcid.org/0000-0002-5307-3858
authors.initials: B
authors.lastname: Westerlund-Wikström
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D005341:Fibrinolysin / Q000378:metabolism; D006801:Humans; D055767:Immobilized Proteins / Q000378:metabolism; D046915:Penicillin-Binding Proteins / Q000378:metabolism*; D010958:Plasminogen / Q000378:metabolism*; D011485:Protein Binding; D011994:Recombinant Proteins / Q000378:metabolism; D012995:Solubility; D013211:Staphylococcus aureus / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D055767:Immobilized Proteins; D046915:Penicillin-Binding Proteins; D011994:Recombinant Proteins; D010958:Plasminogen; D005341:Fibrinolysin
keywords: Adhesion; Penicillin binding protein; Plasmin; Plasminogen; Staphylococcus aureus