New antigenic regions of streptokinase are identified by affinity-directedmass spectrometry

Streptokinase (SK) is a bacterial protein used for the treatment of myocard ial infarction, which is immunogenic in humans. Here we report the use of a n 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 locat ed three previously identified antigenic regions and have now mapped them a nd shown that they can be defined more precisely as residues P4-L8, P171-P1 77 and K334-N338.