NMR SECONDARY STRUCTURE OF THE PLASMINOGEN-ACTIVATOR PROTEIN STAPHYLOKINASE

Staphylokinase (Sak) is a 15.5 kDa protein secreted by several strains of Staphylococcus aureus. Due to its ability to convert plasminogen, the inactive proenzyme of the fibrinolytic system, into plasmin, Sak i s presently undergoing clinical trials for blood clot lysis in the tre atment of thrombovascular disorders. With a view to developing a bette r understanding of the mode of action of Sak, we have initiated a stru ctural investigation of Sak via multidimensional heteronuclear NMR spe ctroscopy employing uniformly N-15- and N-15,C-13-labelled Sak. Sequen ce-specific resonance assignments have been made employing N-15-edited TOCSY and NOE experiments and from HNCACB, CBCA(CO)NH, HBHA(CBCACO)NH and CC(CO)NH sets of experiments. From an analysis of the chemical sh ifts, (3)J(H)N(H) alpha scalar coupling constants, NOEs and H-N exchan ge data, the secondary structural elements of Sak have been characteri zed.