Key words: Peptidyl prolyl cis/trans isomerases; Cyclosporin A; FK506; Immunosuppression; Protein folding; Signal transduction
Peptidyl prolyl cis/trans isomerases (PPIases) make up a novel class of enzymes which are able to catalyse the cis/trans isomerisation of Xaa-Pro bonds in proteins. Due to this activity they are able to accelerate the folding of proteins either after translation at the ribosome or after traversal of intracellular membranes. Three families of PPIases are known to date: Cyclophilins, FKBPs and parvulins. All PPIases of a cell can make up 2 % of total protein. PPIases are present in every living cell from E. coli to man. Cyclophilins bind the clinical important immunosuppressant Cyclosporin A (CsA); FKBPs bind the immunosuppressants FK506/Rapamycin. A cytosolic cyclophilin and a cytosolic FKBP mediate the immunosuppressive effects of CsA resp. FK506/rapamycin.
Our laboratory investigates the regulation, cellular functions and mechanisms of different PPIases in N. crassa, S. cerevisiae and C. elegans. We were the first group showing that a cytosolic cyclophilin mediates the CsA effect in the fungi Neurospora crassa and Saccharomyces cerevisiae.
The aim is to elucidate
(i) the in vivo roles of different PPIases in protein folding in the cytosol, mitochondria and ER
(ii) the role of PPIases in signal transduction
(iii) the functional interaction of PPIases with molecular chaperones like Hsp90 and Hsp70.