title: Cyclophilin active site mutants have native prolyl isomerase activity with a protein substrate.
abstract: The prolyl isomerase activity of cyclophilins is traditionally measured by an assay in which prolyl cis/trans isomerization in a chromogenic tetrapeptide is coupled with its isomer-specific cleavage by chymotrypsin. Two variants of mitochondrial cyclophilin with substitutions in the presumed active site (R73A and H144Q) are inactive in the protease-coupled assay, but show almost wild-type activity in an assay that is based on the catalysis of a proline-limited protein folding reaction. This prolyl isomerase assay is preferable, both because coupling with proteolysis is avoided and because an intact protein instead of a short peptide is used as a substrate. Possibly, some earlier conclusions about the catalytic mechanism and the involvement of the prolyl isomerase activity in the cellular function of immunophilins may need reevaluation.
authors.affiliation: Biochemisches Laboratorium, Universität Bayreuth, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Scholz
authors.forename: T
authors.initials: T
authors.lastname: Schindler
authors.forename: K
authors.initials: K
authors.lastname: Dolinski
authors.forename: J
authors.initials: J
authors.lastname: Heitman
authors.forename: F X
authors.initials: FX
authors.lastname: Schmid
mesh_terms: D000591:Amino Acid Isomerases / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002918:Chymotrypsin / Q000378:metabolism; D010450:Endopeptidases / Q000378:metabolism; D005656:Fungal Proteins / Q000378:metabolism; D007700:Kinetics; D008928:Mitochondria / Q000201:enzymology; D009154:Mutation; D010455:Peptides / Q000378:metabolism; D019696:Peptidylprolyl Isomerase; D017510:Protein Folding; D011506:Proteins / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D013053:Spectrophotometry
chemical_list: D002352:Carrier Proteins; D005656:Fungal Proteins; D010455:Peptides; D011506:Proteins; D010450:Endopeptidases; D002918:Chymotrypsin; D000591:Amino Acid Isomerases; D019696:Peptidylprolyl Isomerase