Purification and properties of multiple molecular forms of yeast peptidyl prolyl cis-trans isomerase

By hydrophobic chromatography on a butyl-Toyopearl 650 M column, yeast peptidyl prolyl cis-trans isomerase (PPIase) was separated into at least three molecular components (PPI-I, PPI-II and PPI-III) in their native forms. On the basis of the result of SDS-PAGE, PPI-II and PPI-III were highly purified and their molecular masses were estimated to be 16.5 and 17.2 kDa, respectively. However, PPI-I was still a mixture of two components with molecular masses of 23.3 and 24.1 kDa. The UV absorption spectrum of PPI-II was slightly different from that of PPI-III. In contrast, the CD spectra of the two proteins were essentially identical in the far-UV region. Upon addition of an immunosuppressant, cyclosporine A (CsA), the absorption spectra of the two highly purified proteins were subtly changed, which was indicative of some alterations in the microenvironments of the aromatic amino-acid residues. The two proteins exhibited subtle but clear differences in the kinetic parameters (kc/Km) for the PPIase-catalyzed cis-trans isomerization and in the inhibition constants of CsA for the PPIase activity. These results lead to the conclusions that (1), a family of PPIases exists in one organism and that (2), one member of the family has multiple molecular forms with different substrate specificities and different affinities for the drugs (inhibitors).