NMR secondary structure of the plasminogen activator protein staphylokinase

Staphylokinase (Sak) is a 15.5 kDa protein secreted by several strains of Staphylococcusaureus. Due to its ability to convert plasminogen, the inactive proenzyme of the fibrinolyticsystem, into plasmin, Sak is presently undergoing clinical trials for blood clot lysis in thetreatment of thrombovascular disorders. With a view to developing a better understanding ofthe mode of action of Sak, we have initiated a structural investigation of Sak viamultidimensional heteronuclear NMR spectroscopy employing uniformly 15N- and 15N,13C-labelled Sak. Sequence-specific resonance assignments have been made employing 15N-editedTOCSY and NOE experiments and from HNCACB, CBCA(CO)NH, HBHA(CBCACO)NHand CC(CO)NH sets of experiments. From an analysis of the chemical shifts,3JHNH scalar coupling constants, NOEs and HN exchange data, the secondary structural elements of Sakhave been characterized.