The protein phosphatase 2A phosphatase activator is a novel peptidyl-prolyl cis/trans-isomerase.
The protein phosphatase 2A (PP2A) phosphatase activator (PTPA) is an essential protein involved in the regulation of PP2A and the PP2A-like enzymes. In this study we demonstrate that PTPA and its yeast homologues Ypa1 and Ypa2 can induce a conformational change in some model substrates. Using these model substrates in different assays with and without helper proteases, this isomerase activity is similar to the isomerase activity of FKBP12, the human cyclophilin A, and one of its yeast homologs Cpr7 but dissimilar to the isomerase activity of Pin1. However, neither FKBP12 nor Cpr7 can reactivate the inactive form of PP2A. Therefore, PTPA belongs to a novel peptidyl-prolyl cis/trans-isomerase (PPIase) family. The PPIase activity of PTPA correlates with its activating activity since both are stimulated by the presence of Mg2+ATP, and a PTPA mutant (Delta208-213) with 400-fold less activity in the activation reaction of PP2A also showed almost no PPIase activity. The point mutant Asp205 --> Gly (in Ypa1) identified this amino acid as essential for both activities. Moreover, PTPA dissociates the inactive form from the complex with the PP2A methylesterase. Finally, Pro190 in the catalytic subunit of PP2A (PP2AC) could be identified as the target Pro isomerized by PTPA/Mg2+ATP since among the 14 Pro residues present in 12 synthesized peptides representing the microenvironments of these prolines in PP2AC, only Pro190 could be isomerized by PTPA/Mg2+ATP. This Pro190 is present in a predicted loop structure near the catalytic center of PP2AC and, if mutated into a Phe, the phosphatase is inactive and can no longer be activated by PTPA/Mg2+ATP.
Jordens
Jan
J
Afdeling Biochemie, Faculteit Geneeskunde, Katholieke Universiteit Leuven, Campus Gasthuisberg, Herestraat 49, B-3000 Leuven, Belgium.
Janssens
Veerle
V
Longin
Sari
S
Stevens
Ilse
I
Martens
Ellen
E
Bultynck
Geert
G
Engelborghs
Yves
Y
Lescrinier
Eveline
E
Waelkens
Etienne
E
Goris
Jozef
J
Van Hoof
Christine
C
D000255:Adenosine Triphosphate / Q000502:physiology; D000818:Animals; D019556:COS Cells; D020134:Catalytic Domain; D002522:Chlorocebus aethiops; D021984:Cyclophilin A / Q000235:genetics / Q000502:physiology; D000081406:Peptidyl-Prolyl Isomerase F; D021983:Cyclophilins / Q000235:genetics / Q000502:physiology; D006801:Humans; D007700:Kinetics; D008274:Magnesium / Q000502:physiology; D005810:Multigene Family; D016297:Mutagenesis, Site-Directed; D000072340:NIMA-Interacting Peptidylprolyl Isomerase; D019696:Peptidylprolyl Isomerase / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011392:Proline / Q000235:genetics / Q000378:metabolism; D054648:Protein Phosphatase 2; D011506:Proteins / Q000235:genetics / Q000502:physiology*; D011817:Rabbits; D013379:Substrate Specificity; D022061:Tacrolimus Binding Protein 1A / Q000235:genetics / Q000502:physiology
D000081406:Peptidyl-Prolyl Isomerase F; D000072340:NIMA-Interacting Peptidylprolyl Isomerase; D011506:Proteins; D000255:Adenosine Triphosphate; D011392:Proline; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; D021984:Cyclophilin A; D021983:Cyclophilins; D022061:Tacrolimus Binding Protein 1A; C000606846:PIN1 protein, human; C087440:PTPA protein, human; D019696:Peptidylprolyl Isomerase; D008274:Magnesium