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.