CONFORMATION AND STABILITY OF STREPTOKINASES FROM NEPHRITOGENIC AND NONNEPHRITOGENIC STRAINS OF STREPTOCOCCI

Conformation and stability of three Sks hom Streptococcus equisimilis strain H46A, Streptococcus pyogenes strain A374, and Streptococcus pyo genes strain AT27 were compared by Limited proteolysis, CD, and fluore scence measurements and by DSC. The general similarity of the peptide CD spectra in the spectral region 185 to 260 nm indicates the same typ e of folding for the three proteins. Fluorescence and aromatic CD spec tra are consistent with a predominant surface localization of the arom atic amino acids and a low rigidity of their surroundings. A major dif ference among the three Sks is shown by deconvolution of their excessi ve heat capacity functions. Deconvolution reveals two energetic foldin g units in Sk H46A but three energetic folding units in Sk A374 and Sk AT27. Digestion of the Sks with trypsin indicates a reduced sensitivi ty of the C-terminal region of Sk A374 and Sk AT27 in comparison to Sk H46A. This suggests that amino acids of the C-terminal region partici pate in the formation of the third folding unit of Sk A374 and Sk AT27 . Proteins 27:26-35 (C) 1997 Wiley-Liss, Inc.