title: Multiple interactions of FbsA, a surface protein from Streptococcus agalactiae, with fibrinogen: affinity, stoichiometry, and structural characterization.
abstract: Streptococcus agalactiae is an etiological agent of several infective diseases in humans. We previously demonstrated that FbsA, a fibrinogen-binding protein expressed by this bacterium, elicits a fibrinogen-dependent aggregation of platelets. In the present communication, we show that the binding of FbsA to fibrinogen is specific and saturable, and that the FbsA-binding site resides in the D region of fibrinogen. In accordance with the repetitive nature of the protein, we found that FbsA contains multiple binding sites for fibrinogen. By using several biophysical methods, we provide evidence that the addition of FbsA induces extensive fibrinogen aggregation and has noticeable effects on thrombin-catalyzed fibrin clot formation. Fibrinogen aggregation was also found to depend on FbsA concentration and on the number of FbsA repeat units. Scanning electron microscopy evidentiated that, while fibrin clot is made of a fine fibrillar network, FbsA-induced Fbg aggregates consist of thicker fibers organized in a cage-like structure. The structural difference of the two structures was further indicated by the diverse immunological reactivity and capability to bind tissue-type plasminogen activator or plasminogen. The mechanisms of FbsA-induced fibrinogen aggregation and fibrin polymerization followed distinct pathways since Fbg assembly was not inhibited by GPRP, a specific inhibitor of fibrin polymerization. This finding was supported by the different sensitivity of the aggregates to the disruptive effects of urea and guanidine hydrochloride. We suggest that FbsA and fibrinogen play complementary roles in contributing to thrombogenesis associated with S. agalactiae infection.
authors.affiliation: Department of Biochemistry, University of Pavia, Viale Taramelli 3/B 27100 Pavia, Italy.
authors.forename: Giampiero
authors.initials: G
authors.lastname: Pietrocola
authors.forename: Livia
authors.initials: L
authors.lastname: Visai
authors.forename: Viviana
authors.initials: V
authors.lastname: Valtulina
authors.forename: Emanuele
authors.initials: E
authors.lastname: Vignati
authors.forename: Simonetta
authors.initials: S
authors.lastname: Rindi
authors.forename: Carla Renata
authors.initials: CR
authors.lastname: Arciola
authors.forename: Roberto
authors.initials: R
authors.lastname: Piazza
authors.forename: Pietro
authors.initials: P
authors.lastname: Speziale
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D001665:Binding Sites; D001777:Blood Coagulation; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism*; D003001:Cloning, Molecular; D004926:Escherichia coli; D005337:Fibrin; D005340:Fibrinogen / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008855:Microscopy, Electron, Scanning; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D013292:Streptococcus agalactiae / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; C499709:FbsA protein, Streptococcus agalactiae; D010446:Peptide Fragments; D011994:Recombinant Proteins; D005337:Fibrin; D005340:Fibrinogen