Enhanced activation of bound plasminogen on Staphylococcus aureus by staphylokinase

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Abstract
Activation of plasminogen (plg) to plasmin by the staphylococcal activator, staphylokinase (SAK), is effectively regulated by the circulating inhibitor, α2-antiplasmin (α2AP). Here it is demonstrated that intact Staphylococcus aureus cells and solubilized staphylococcal cell wall proteins not only protected SAK-promoted plg activation against the inhibitory effect of α2AP but also enhanced the activation. The findings suggest that the surface-associated plg activation by SAK may have an important physiological function in helping staphylococci in tissue dissemination. Amino acid sequencing of tryptic peptides originating from the 59-, 56- and 43-kDa proteins, isolated as putative plg-binding proteins, identified them as staphylococcal inosine 5′-monophosphate dehydrogenase, α-enolase, and ribonucleotide reductase subunit 2, respectively.