Staphylokinase

Staphylokinase (SAK; also known as staphylococcal fibrinolysin or Müller's factor) is a protein produced by Staphylococcus aureus. It contains 136 amino acid residues and has a molecular mass of 15kDa. Synthesis of staphylokinase occurs in late exponential phase. It is similar to streptokinase.

Staphylokinase is positively regulated by the "agr" gene regulator. It activates plasminogen to form plasmin, which digests fibrin clots. This disrupts the fibrin meshwork which forms to keep infections localized. Staphylokinase interacts with plasminogen to form a 1:1 complex that exposes the active site of the plasminogen molecule. The plasmin Sak complex is neutralized by α2- antiplasmin in plasma in the absence of fibrin, resulting in lysis. However, in the presence of fibrin, the inhibition is delayed, creating a unique mechanism for fibrin selectivity in plasma.