Expression and characterization of the intact N-terminal domain of streptokinase

Proteolytic studies have enabled two of the three putative domains of the f ibrinolytic protein streptokinase to be isolated and characterized (Conejer o-Lara F et al., 1996, Protein Sci 5:2583-2591). The N-terminal domain, how ever, could not be isolated in these experiments because of its susceptibil ity to proteolytic cleavage. To complete the biophysical characterization o f the domain structure of streptokinase we have overexpressed, purified, an d characterized the N-terminal region of the protein, residues 1-146. The r esults show this is cooperatively folded with secondary structure content a nd overall stability closely similar to those of the equivalent region in t he intact protein.