New antigenic regions of streptokinase are identified by affinity-directed mass spectrometry.

Streptokinase (SK) is a bacterial protein used for the treatment of myocardial infarction, which is immunogenic in humans. Here we report the use of an affinity-directed MS approach to determine the minimal epitopes involved in the binding between SK and patient antibodies. Using this method we have identified two novel epitopes and mapped these to the minimal recognition regions formed by the amino acids D96-E99 and F323-D328. We have also located three previously identified antigenic regions and have now mapped them and shown that they can be defined more precisely as residues P4-L8, P171-P177 and K334-N338.