title: Streptokinase variants from Streptococcus pyogenes isolates display altered plasminogen activation characteristics - implications for pathogenesis.
abstract: Streptococcus pyogenes (group A streptococcus, GAS) secretes streptokinase, a potent plasminogen activating protein. Among GAS isolates, streptokinase gene sequences (ska) are polymorphic and can be grouped into two distinct sequence clusters (termed cluster type-1 and cluster type-2) with cluster type-2 being further divided into sub-clusters type-2a and type-2b. In this study, far-UV circular dichroism spectroscopy indicated that purified streptokinase variants of each type displayed similar secondary structure. Type-2b streptokinase variants could not generate an active site in Glu-plasminogen through non-proteolytic mechanisms while all other variants had this capability. Furthermore, when compared with other streptokinase variants, type-2b variants displayed a 29- to 35-fold reduction in affinity for Glu-plasminogen. All SK variants could activate Glu-plasminogen when an activator complex was preformed with plasmin; however, type-2b and type-1 complexes were inhibited by α(2) -antiplasmin. Exchanging ska(type-2a)  in the M1T1 GAS strain 5448 with ska(type-2b)  caused a reduction in virulence while exchanging ska(type-2a)  with ska(type-1)  into 5448 produced an increase in virulence when using a mouse model of invasive disease. These findings suggest that streptokinase variants produced by GAS isolates utilize distinct plasminogen activation pathways, which directly affects the pathogenesis of this organism.
authors.affiliation: Illawarra Health and Medical Research Institute, School of Biological Sciences, University of Wollongong, Wollongong, Australia.
authors.forename: Simon M
authors.initials: SM
authors.lastname: Cook
authors.forename: Amanda
authors.initials: A
authors.lastname: Skora
authors.forename: Christine M
authors.initials: CM
authors.lastname: Gillen
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Walker
authors.forename: Jason D
authors.initials: JD
authors.lastname: McArthur
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D020134:Catalytic Domain; D014644:Genetic Variation; D006801:Humans; D051379:Mice; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D009154:Mutation; D010958:Plasminogen / Q000737:chemistry / Q000378:metabolism*; D010960:Plasminogen Activators; D017422:Sequence Analysis, DNA; D013290:Streptococcal Infections / Q000382:microbiology / Q000401:mortality*; D013297:Streptococcus pyogenes / Q000201:enzymology / Q000235:genetics / Q000472:pathogenicity*; D013300:Streptokinase / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D014774:Virulence
chemical_list: D010958:Plasminogen; D013300:Streptokinase; D010960:Plasminogen Activators