title: Characterization of streptokinases from group A Streptococci reveals a strong functional relationship that supports the coinheritance of plasminogen-binding M protein and cluster 2b streptokinase.
abstract: Group A streptococcus (GAS) strains secrete the protein streptokinase (SK), which functions by activating host human plasminogen (hPg) to plasmin (hPm), thus providing a proteolytic framework for invasive GAS strains. The types of SK secreted by GAS have been grouped into two clusters (SK1 and SK2) and one subcluster (SK2a and SK2b). SKs from cluster 1 (SK1) and cluster 2b (SK2b) display significant evolutionary and functional differences, and attempts to relate these properties to GAS skin or pharynx tropism and invasiveness are of great interest. In this study, using four purified SKs from each cluster, new relationships between plasminogen-binding group A streptococcal M (PAM) protein and SK2b have been revealed. All SK1 proteins efficiently activated hPg, whereas all subclass SK2b proteins only weakly activated hPg in the absence of PAM. Surface plasmon resonance studies revealed that the lower affinity of SK2b to hPg served as the basis for the attenuated activation of hPg by SK2b. Binding of hPg to either human fibrinogen (hFg) or PAM greatly enhanced activation of hPg by SK2b but minimally influenced the already effective activation of hPg by SK1. Activation of hPg in the presence of GAS cells containing PAM demonstrated that PAM is the only factor on the surface of SK2b-expressing cells that enabled the direct activation of hPg by SK2b. As the binding of hPg to PAM is necessary for hPg activation by SK2b, this dependence explains the coinherant relationship between PAM and SK2b and the ability of these particular strains to generate the proteolytic activity that disrupts the innate barriers that limit invasiveness.
authors.affiliation: W. M. Keck Center for Transgene Research and Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, USA. .
authors.forename: Yueling
authors.initials: Y
authors.lastname: Zhang
authors.forename: Zhong
authors.initials: Z
authors.lastname: Liang
authors.forename: Hsing-Tse
authors.initials: HT
authors.lastname: Hsueh
authors.forename: Victoria A
authors.initials: VA
authors.lastname: Ploplis
authors.forename: Francis J
authors.initials: FJ
authors.lastname: Castellino
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D004789:Enzyme Activation / Q000235:genetics; D006801:Humans; D008969:Molecular Sequence Data; D010958:Plasminogen / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D059748:Proteolysis; D012756:Sheep; D013290:Streptococcal Infections / Q000235:genetics / Q000378:metabolism; D013297:Streptococcus pyogenes / Q000201:enzymology* / Q000235:genetics / Q000472:pathogenicity; D013300:Streptokinase / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; C084529:plasminogen-binding protein, bacteria; D010958:Plasminogen; D013300:Streptokinase