Staphylokinase (SAK; also known as staphylococcal fibrinolysin or Müller's factor) is a protein produced by Staphylococcus aureus.
[1] The plasmin Sak complex is neutralized by α2- antiplasmin in plasma in the absence of fibrin, resulting in lysis.
[citation needed] Staphylokinase also cleaves IgG and complement component C3b, inhibiting phagocytosis.
The first 27 amino acids code for a signal peptide which is cleaved off in the mature protein (mSak).
When in solution, this position varies between the two domains suggesting a flexible dumbbell shape.