The protein interaction of Saccharomyces cerevisiae cytoplasmic thiol peroxidase II with SFH2p and its in vivo function.

Previously, we reported that the yeast cytoplasmic thiol peroxidase type II isoform (cTPx II), a member of the TSA/AhpC family, showed a very low peroxidase activity when compared with other cytoplasmic yeast isoforms, and that cTPx II mutant (cTPx II Delta) showed a severe growth retardation compared with that of the wild-type cells. To reveal the physiological function of cTPx II in yeast cell growth, we searched for proteins which react with cTPx II. In this study, we identified a novel interaction between cTPx II and CSR1p using the yeast two-hybrid system. CSR1p (SFH2p) has been known to be one member of Sec14 homologous (SFH2) proteins. SFH2p exhibits phosphatidylinositol transfer protein activity. Interestingly, we found that cTPx II selectively bound to SFH2p among the five types of SFH proteins and Sec14p. The interaction required the dimerization of cTPx II. In addition, SFH2p also specifically bound to cTPx II among the yeast thiol peroxidase isoforms. The selective interaction of the dimer form of cTPx II (the oxidized form) with SFH2p was also confirmed by glutathione S-transferase pull-down and immunoprecipitation assays. The growth retardation, clearly reflected by the length of the lag phase, of cTPx II Delta was rescued by deleting SFH2p in the cTPx II Delta strain. The SFH2 Delta strain did not show any growth retardation. In addition, the double mutant showed a higher susceptibility to oxidative stress. This finding provides the first in vivo demonstration of the specific interaction of cTPx II with SFH2p in an oxidative stress-sensitive manner and a novel physiological function of the complex of cTPx II and SFH2p.