The β‐domain of streptokinase affects several functionalities, including specific/proteolytic activity kinetics

Abstract

Streptokinase (SK) is a plasminogen activator which converts inactive plasminogen (Pg) to active plasmin (Pm), which cleaves fibrin clots. SK secreted by groups A, C, and G Streptococcus (SKA/SKC/SKG) is composed of three domains: SKα, SKβ and SKγ. Previous domain‐swapping studies between SK1/SK2b‐cluster variants revealed that SKβ plays a major role in the activation of human Pg. Here, we carried out domain‐swapping between skcg ‐SK/SK2‐cluster variants to determine the involvement of SKβ in several SK functionalities, including specific/proteolytic activity kinetics, fibrinogen‐bound Pg activation and α 2 ‐antiplasmin resistance. Our results indicate that SKβ has a minor to determining role in these diverse functionalities for skcg ‐SK and SK2b variants, which might potentially be accompanied by few critical residues acting as hot spots. Our findings enhance our understanding of the roles of SKβ and hot spots in different functional characteristics of SK clusters and may aid in the engineering of fibrin‐specific variants of SK for breaking down blood clots with potentially higher efficacy and safety.

Lysine Residues in the MK-Rich Region Are Not Required for Binding of the PbsP Protein From Group B Streptococci to Plasminogen

“…LBS in Kringle domains bind free lysine and EACA in the following order of affinity: K1 > K4 > K5 > K2 ( Lin et al., 2000 ; Sun et al., 2002 ) while the K3 domain displays only slight lysine-binding activity. Streptokinase and staphylokinase are extracellularly secreted products of, respectively, Streptoccoccus pyogenes and Staphylococcus aureus that directly bind and activate Plg ( Verhamme and Bock, 2014 ; Verhamme et al., 2015 ; Nguyen and Vogel, 2016 ; Rafipour et al., 2019 ). Other extracellular proteins, such as Skizzle from GBS, and surface-associated Plg-binding bacterial products (often referred to as bacterial Plg receptors), rely instead on external activators, such as host-derived uPA or tPA, for conversion of bound Plg into Pl ( Wiles et al., 2010 ; Peetermans et al., 2016 ).…”