Native recombinant cyclophilins A, B, and C degrade DNA independently of peptidylprolyl cis-trans-isomerase activity. Potential roles of cyclophilins in apoptosis

Previous work in our laboratory (Montague, J., Gaido, M., Frye, C., and Cidlowski, J. (1994) J. Biol. Chem. 269, 18877-18880) has shown that human recombinant cyclophilins A, B, and C have sequence homology with the apoptotic nuclease NUC18 and that denatured cyclophilins can degrade DNA. We have now evaluated the nucleolytic activity of recombinant cyclophilins under native conditions. We show that nuclease activity inherent to cyclophilins is distinct from cis-trans-peptidylprolyl isomerase activity and is similar to that described for apoptotic nucleases. Cyclophilin nucleolytic activity is stimulated by Ca2+ and/or Mg2+, with a combination of the two being optimal for cyclophilins A and B. Mg2+ alone is sufficient for cyclophilin C nuclease activity. pH optimums are in the range of pH 7.5-9.5. Cyclophilins can degrade both single-stranded and double-stranded DNA. Additionally, cyclophilins produce 3'-OH termini in linear double-stranded substrates, suggesting the cuts produced are similar to those of apoptotic cells. Cyclophilins also display endonucleolytic activity, demonstrated by their ability to degrade supercoiled DNA. In the absence of ions, cyclophilins bind linearized DNA. When added to nuclei from nonapoptotic cells, cyclophilin C induces 50-kilobase pair DNA fragmentation but not internucleosomal fragmentation. Together, these data suggest that cyclophilins are involved in degradation of the genome during apoptosis.

Cooperation of enzymatic and chaperone functions of trigger factor in the catalysis of protein folding

The trigger factor of Escherichia coli is a prolyl isomerase and accelerates proline-limited steps in protein folding with a very high efficiency. It associates with nascent polypeptide chains at the ribosome and is thought to catalyse the folding of newly synthesized proteins. In its enzymatic mechanism the trigger factor follows the Michaelis-Menten equation. The unusually high folding activity of the trigger factor originates from its tight binding to the folding protein substrate, as reflected in the low Km value of 0.7 microM. In contrast, the catalytic constant kcat is small and shows a value of 1.3 s(-1) at 15 degrees C. An unfolded protein inhibits the trigger factor in a competitive fashion. The isolated catalytic domain of the trigger factor retains the full prolyl isomerase activity towards short peptides, but in a protein folding reaction its activity is 800-fold reduced and no longer inhibited by an unfolded protein. Unlike the prolyl isomerase site, the polypeptide binding site obviously extends beyond the FKBP domain. Together, this suggests that the good substrate binding, i.e. the chaperone property, of the intact trigger factor is responsible for its high efficiency as a catalyst of proline-limited protein folding.

Modulation of cyclosporin A/cyclophilin interactions by drug vehicles

Cyclosporin A (CsA) is a tight-binding inhibitor of the peptidyl-prolyl cis/trans isomerase (PPIase) activity of human cytosolic cyclophilin (Cyp18), the putative receptor for immunosuppressive effects of the drug. We examined the influence of cremophor EL (CEL), a surfactant that has found wide use for CsA formulation, on the kinetics of inhibition of the enzyme by CsA. Stock solutions of CsA in CEL administered into aqueous PPIase assays led to inhibition kinetics reminiscent to those of CsA dissolved in tetrahydrofurane, but caused an increase in the final Ki value of about sevenfold at 0.33% (v/v) CEL. The diminished drug affinity to Cyp18 obtained in experiments using CEL could also be established for analogues of cyclosporin A such as [Ala2]-Cs,[Thr2]-Cs, and [MeAla6]-Cs, exhibiting Ki values 13-16-fold higher than in the absence of CEL. In addition, the time-dependent pattern of inhibition indicate only a minor population of bioactive conformation of CsA in bulky CEL. Conformational reshuffling of the bioinactive [cis-MeLeu9-MeLeu10]-Cs to create an inhibitory fraction of the drug was delayed in the presence of CEL micelles, despite potential ability of micelles exists to catalyze cis/trans isomerizations of N-alkyl peptide bonds. The pattern of inhibition when using cyclophilins distinct in their amino acid sequences to the human enzyme can be rationalized in terms of exceptional high structural requirements of human Cyp18 for the drug conformation.

Chaperone function of Hsp90-associated proteins

The Hsp90 heat shock protein of eukaryotic cells regulates the activity of proteins involved in signal transduction pathways and may direct intracellular protein folding in general. Hsp90 performs at least part of its function in a complex with a specific set of partner proteins that include members of the prolyl isomerase family. The properties of the major components of the Hsp90 complex were examined through the use of in vitro protein folding assays. Two of the components, FKBP52 and p23, functioned as mechanistically distinct molecular chaperones. These results suggest the existence of a super-chaperone complex in the cytosol of eukaryotic cells.

Carboxymethylation of MutS-cysteine-15 specifically inactivates adenosylcobalamin-dependent glutamate mutase. Examination of the role of this residue in coenzyme-binding and catalysis

The sensitivity of adenosylcobalamin (AdoCbl)-dependent glutamate mutase toward thiol-directed reagents has been investigated. Iodoacetate specifically alkylates one cysteine residue, Cys-15, in MutS with concomitant irreversible loss of enzyme activity. Cys-15 lies between the conserved residues Asp-14 and His-16, that are believed to coordinate cobalt to form a Co-His-Asp hydrogen-bonded "triad" when AdoCbl is bound by the enzyme. Although inactive, carboxymethylated MutS still bound AdoCbl with only a 5-fold increase in apparent Kd. To determine whether Cys-15 plays an essential role in catalysis, it was mutated to serine and to alanine. These mutants were active, but both exhibited decreased Vmax and increased apparent Km and Kd for AdoCbl. To mimic the effect of carboxymethylation, Cys15 was mutated to aspartate and, as an isosteric control, to asparagine. Neither of these mutants was active: MutS-C15N bound AdoCbl approximately 10-fold weaker than wild type, whereas MutS-C15N bound AdoCbl over 100 times less strongly than wild type. The results demonstrate both coenzyme-binding and catalysis to be very sensitive to mutations at position 15 that could potentially perturb the Co-His-Asp hydrogen-bonding network.

A novel plant peptidyl-prolyl-cis-trans-isomerase (PPIase): cDNA cloning, structural analysis, enzymatic activity and expression

A novel cDNA encoding for a peptidyl-prolyl-cis-trans-isomerase (PPIase) belonging to the FK506-binding protein (FKBP) family was isolated from wheat. It contains an open reading frame of 559 amino acids and it represents the first plant FKBP-PPIase to be cloned. It possesses a unique sequence which is composed of three FKPB-like domains, in addition to a putative tetratricopeptide repeat (TPR) motif and a calmodulin-binding site. The recombinant FKBP-PPIase expressed in and purified from Escherichia coli exhibits PPIase activity that is efficiently inhibited by the immunosuppressive drugs FK506 and rapamycin. Northern blot analysis showed that wheat FKBP was found mainly in young tissues. Polyclonal antibodies revealed the presence of cross-reacting proteins in embryos, roots and shoots. The unique structural features, the enzymatic activity and the presence of putative isoforms in wheat tissues indicate the possibility of the involvement of wheat PPIase in essential biological functions, similar to other members of the FKBP gene family.

Inhibition of HIV-1 replication by cyclosporine A or related compounds correlates with the ability to disrupt the Gag-cyclophilin A interaction

The HIV-1 Gag polyprotein specifically incorporates the cellular peptidylprolyl isomerase cyclophilin A into virions. HIV-1 replication is inhibited by cyclosporine A, an immunosuppressive drug which binds with high affinity to cyclophilin A and precludes interaction with the Gag polyprotein. Using a panel of four drugs, including cyclosporine A, two nonimmunosuppressive analogues of cyclosporine A which bind to cyclophilin A but which cannot form a tertiary complex with the calcium-dependent phosphatase calcineurin, and the structurally unrelated immunosuppressant FK506, we demonstrated that the antiviral effect of cyclosporine A is not due to blockade of calcineurin-mediated signal transduction pathways. Rather, the effectiveness of cyclosporine A and related compounds at inhibiting HIV-1 replication correlates with cyclophilin A-binding affinity and with the ability to disrupt the interaction between cyclophilin A and the HIV-1 Gag polyprotein. These results support the contention that the Gag-cyclophilin A interaction is required for HIV-1 replication.

Involvement of the N-terminal part of cyclophilin B in the interaction with specific Jurkat T-cell binding sites

Cyclophilin B (CyPB) is secreted in biological fluids such as blood or milk and binds to a specific receptor present on the human lymphoblastic cell line Jurkat and on human peripheral blood lymphocytes. This study was intended to specify the areas of CyPB that are involved in the interaction with the receptor. A synthetic peptide corresponding to the first 24 N-terminal amino acid residues of CyPB was shown to specifically recognize the receptor. Moreover, modification of Arg18 of CyPB by p-hydroxyphenlglyoxal led to a dramatic loss of affinity for the receptor. However, when this residue was replaced by an alanine residue using site-directed mutagenesis, no modification of the binding properties was found, suggesting that Arg18 is not directly involved but is sufficiently close to the interaction site to interfere with the binding when modified. Competitive binding experiments using a chimaeric protein made up of the 24 N-terminal amino acid residues of CyPB fused to the cyclophilin A core sequence confirmed the involvement of this region of CyPB in receptor binding.

A large-scale processing of kinetic data files with derivation of the inhibitory constant Ki: an application to proline isomerases

An integral system of algorithms (file preprocessor + the adapted KORE program + the Powell non-linear least-squares minimizer) named KINMIN is described. This system was applied to simultaneously process a large number of kinetic data files for cis/trans isomerization of Xaa-Pro bonds in synthetic peptides catalysed by peptidylproline cis/trans isomerases which can be inhibited by nanomolar concentrations of the immunosuppressive compounds cyclosplorin-A, FK506 or rapamycin. The system allows preprocessing of kinetics data files and derives from them the first-order rate constants which are used to optimize the inhibitory constant Ki of each inhibitor. The KINMIN program may be also applied to derive Ki for other sets of enzymes and their inhibitors.

Purification and characterization of cytosolic and microsomal cyclophilins from maize (Zea mays)

Methods for the purification and separation of peptidyl prolyl cis-trans isomerase (PPI) from cytosolic and microsomal fractions of etiolated maize are described. On SDS/PAGE, the purified preparations appears as single polypeptides with molecular masses of 17.5 kDa and 17.7 kDa respectively. Instead of using immobilized cyclosporin A derivatives as affinity adsorbents, our methods employ conventional techniques enabling purification of the proteins on a much larger scale than previously described. An antiserum raised against the cytosolic PPI recognizes polypeptides of similar molecular mass from a wide range of plant species on an immunoblot. There is virtually no recognition of the microsomal PPI. The cytosolic and microsomal PPIs are inhibited by cyclosporin A (Ki = 6 nM in both cases), indicating that they are cyclophilins. The cytosolic enzyme is inactivated by 5 mM N-ethylmaleimide and 2 mM phenylglyoxal. N-terminal sequencing of the microsomal PPI indicates a high level of sequence similarity with the N-terminal sequence of mature animal s-cyclophilin (cyclophilin B).

Structure-based design of novel, urea-containing FKBP12 inhibitors

The structure-based design and subsequent chemical synthesis of novel, urea-containing FKBP12 inhibitors are described. These compounds are shown to disrupt the cis-trans peptidylprolyl isomerase activity of FKBP12 with inhibition constants (Ki,app) approaching 0.10 microM. Analyses of several X-ray crystal structures of FKBP12-urea complexes demonstrate that the urea-containing inhibitors associate with FKBP12 in a manner that is similar to, but significantly different from, that observed for the natural product FK506.

An 11.8 kDa proteolytic fragment of the E. coli trigger factor represents the domain carrying the peptidyl-prolyl cis/trans isomerase activity

The 48 kDa trigger factor (TF) of E. coli was shown to be a peptidyl-prolyl cis/trans isomerase (PPIase). Its location on a ribosomal particle is unique among the PPIases described so far, and suggests a role in de novo protein folding. The trigger factor was investigated with regard to a domain carrying the catalytic activity. An enzymatically active fragment could be isolated after proteolysis by subtilisin. The resulting polypeptide was analysed by N-terminal sequencing and MALDI-TOF mass spectrometry revealing an 11.8 kDa fragment of TF encompassing the amino acid residues Arg-145 to Glu-251. The nucleotide sequence encoding the amino acid residues Met-140 to Ala-250 of the TF was cloned into vector pQE32. After expression in E. coli the resulting His-tagged polypeptide was isolated on an Ni2+-NTA column. Subsequent digestion with subtilisin and anion-exchange chromatography yielded a TF fragment encompassing amino acids Gln-148 to Thr-249. This fragment may represent the catalytic core of TF since PPIase activity with a specificity constant kcat/Km of 1.3 microM(-1) s(-1) could be demonstrated when using Suc-Ala-Phe-Pro-Phe-NH-Np as a substrate. Moreover, as was observed for the complete, authentic TF the PPIase activity of the fragment was not inhibited by the peptidomacrolide FK506.

Molecular mechanisms of new immunosuppressants

Maintenance immunosuppressive drugs act by partially blocking rate-limiting steps in the immune response. The new maintenance immunosuppressive drugs are either inhibitors of de novo synthesis of nucleotides (purines or pyrimidines), or are immunophilin-binding drugs that inhibit signal transduction in lymphocytes. The new inhibitors of de novo nucleotide synthesis include mycophenolate mofetil (MMF), mizoribine (MZ), brequinar (BQR), and leflunomide (LEF). MMF and MZ act to inhibit de novo purine synthesis, by inhibition of inosine monophosphate dehydrogenase (IMPDH). They create a selective immunodeficiency in T and B lymphocytes. MMF is hydrolyzed to mycophenolic acid (MPA), an uncompetitive inhibitor of IMPDH. MPA reduces the pools of guanine nucleotides, and increases some adenine nucleotides, inhibiting the cell cycle. Thus the number of specific effector T and B lymphocytes is reduced by limiting clonal expansion. MZ is a competitive inhibitor of IMPDH, which creates a similar defect. The relative clinical effectiveness of MMF versus MZ is not known. MMF has been approved in a number of countries; MZ has been approved in Japan. The inhibitors of de novo pyrimidine synthesis (BQR, LEF) act on the enzyme dehydroorotate dehydrogenase. Neither is currently in clinical trials in transplantation. The new immunophilin-binding drugs inhibit either the calcium-dependent phosphatase calcineurin (CN) [tacrolimus (or FK-506) and the microemulsion form of cyclosporine (CsA)] or signaling from growth factor receptors [rapamycin (sirolimus)]. Tacrolimus binds to FK binding protein-12 (FKBP-12) to create a complex that inhibits CN. CsA binds to cyclophilin to create a complex that inhibits CN. Inhibition of CN prevents activation of cytokine genes in T cells. The relative clinic effectiveness of tacrolimus versus microemulsion CsA is unknown. Rapamycin inhibits signaling from growth factor receptors, such as IL-2R. Rapamycin binds to FKBP to create a complex that engages proteins called TOR (target of rapamycin), or RAFT (rapamycin and FKBP target), which may be kinases. The result is a block in the ability of cytokine receptors to activate cell cycling, interfering with clonal expression. Deoxyspergualin, a parenteral drug in development for induction or antirejection therapy, may inhibit intracellular chaperoning by Hsc70, a member of the heat shock protein family. It may have its principal effect by inhibiting the activation of transcription factor NF-kappa B in antigen-presenting cells and monocytes.

Cyclosporin analogs modified in the 3,7,8-positions: substituent effects on peptidylprolyl isomerase inhibition and immunosuppressive activity are nonadditive

Four analogs of cyclosporin A (CsA) were synthesized to determine if the biological activities of CsA analogs generated by multiple amino acid replacements are predictable from the effects on biological activity of analogs with single residue changes. CsA analogs [Phe7]CsA (8a), [D-MeAla3,Phe7]CsA (8b), [D-Ser8,Phe7]CsA (8c), and [D-MeAla3,Phe7,D-Ser8]CsA (8d) were designed by modification of positions 3, 7, and 8, which are adjacent to one effector region of the cyclophilin-bound CsA complex. The syntheses of CsA analogs 8a-d were carried out by suitable modifications of the reported strategy. Each analog was characterized by NMR in deuterated chloroform and DMSO solutions, and their biological activities as inhibitors of cis-trans-peptidyl prolyl isomerase (PPIase), inhibitors of proliferation in BDF1 mouse spleen cells stimulated with concanavalin A (Con A), and inhibitors of IL-2 release stimulated with PMA/ionomycin by Jurkat cells were determined. Incorporation of the phenylalanine residue in position 7 diminished activities 5-8-fold. Substitution at position 3 decreased activity nearly 2-fold, and substitution at position 8 did not lower activities. However, when all three modifications (D-MeAla3,Phe7, and D-Ser8) were incorporated into one molecule, the resulting analog, 8d, was found to bind more tightly to cyclophilin than CsA (Ki = 3 +/- 1.5 vs 6 +/- 2 nM) and to produce the full immunosuppressive effect in the other assay systems. Our structure-activity results show that combinations of substitutions that individually lower PPIase or immunosuppressive activity produce fully active analogs when combined in a single compound. These results suggest that other, multimodified CsA derivatives may be discovered that possess excellent or improved immunosuppressive activities even though they contain a substitution that otherwise reduces immunosuppressive activity.

Inhibition of peptidyl-prolyl cis/trans isomerase activity by substrate analog structures: thioxo tetrapeptide-4-nitroanilides

The ubiquitous cyclophilins belong to peptidyl-prolyl cis/trans isomerases (PPIases; EC 5.2.1.8). They are able to catalyze the cis/trans isomerization about peptidyl-prolyl amide bonds. The mode of action of human cytosolic cyclophilin (Cyp18cy) has been studied on substrate analog tetrapeptide-4-nitroanilides containing the thioxo peptidyl-prolyl bond. Five peptides of the general structure Ala-Xaa-psi [CS-N]-Pro-Phe-NH-Np (Xaa = Gly, Ala, (S)-2-aminobutyric acid, Phe, and Leu) containing the thioxo peptidyl-prolyl bond were synthesized. The kcat values for the chymotryptic cleavage of 4-nitroanilide bond of the thioxo tetrapeptide-4-nitroanilides ranged from 1.7 to 9.0 s-1 and were sufficiently high to analyze the conformational equilibria by isomer-specific proteolysis. The rate constants of the cis/trans isomerization of the thioxo peptidyl-prolyl bond were found to be 25-100-fold lower due to the O/S substitution. Cyp18cy binds both thioxo peptides and oxo peptides in similar manner in the active center but cannot utilize the sulfur analogs as substrates. Instead, competitive inhibition occurs, which was further characterized for Ala-Gly-psi[CS-N]-Pro-Phe-NH-Np. The inhibition was nearly independent of the pH value in the range of pH 4.5-9, exhibiting apparent Ki values ranging from 200 to 600 microM. In comparison to Ala-Gly-trans-psi[CS-N]-Pro-Phe-NH-Np, the cis thioxo peptide Ala-Gly-cis-psi[CS-N]-Pro-Phe-NH-Np was found to possess an approximately 30-fold higher affinity for the active site of the enzyme. Thus, in the presence of stoichiometric amounts of Cyp18cy, the total amount of Ala-Leu-cis-psi[CS-N]-Pro-Phe-NH-Np in solution, detectable by isomer-specific proteolysis, was considerably enhanced.

The human erythrocyte membrane contains a novel 12-kDa inositolphosphate-binding protein that is an immunophilin

A 12-kDa inositolphosphate-binding protein has been identified as a component of the human erythrocyte membrane. Its robust peptidylprolyl cis-trans isomerase activity that is strongly inhibited by the immunosuppressant drugs FK506 and rapamycin indicates that it is an immunophilin belonging to the FKBP class. The finding that its peptidylprolyl cis-trans isomerase activity is also strongly inhibited by nanomolar concentrations of the second messengers inositol 1,4,5-trisphosphate (IP3) and inositol 1,3,4,5-tetrakisphosphate (IP4) suggests that IP3 and IP4 could be physiological ligands for this membrane-associated immunophilin.

Specific interaction between cyclophilin and cyclic peptides

Cyclophilin A, a peptidyl-prolyl cis-trans is isomerase that catalyzes the otherwise slow isomerization of Xaa-Pro imidic bond, specifically binds the immunosuppressant cyclosporin A. Herein we report evidence on binding of cyclolinopeptide A and its synthetic analogue, [Aib5,6-D-Ala8]cyclolinopeptide, to bovine cyclophilin A. Binding experiments were monitored by fluorescence, CD, and second-derivative spectroscopies, evidencing no remarkable rearrangement of protein structure organization. The possibility that cyclolinopeptide A could act as a substitute of cyclosporin A in the immunosuppression modulation is also briefly discussed.

Cyclophilin-A is a zinc-dependent DNA binding protein in macrophages

The association of cyclosporin A (CsA) immunosuppression with inhibition of transcription factor-dependent lymphokine gene activation formed the basis of our decision to investigate nuclear-associated Cyp isoforms. Immunofluorescence microscopy of mouse macrophages cell line with a monoclonal antibody mAb7F1 raised against CypA shows a co-localisation of CypA in the nucleus and in the cytosol. Nuclear CypA binds to DNA in a zinc ion-dependent manner, in contrast to recombinant CypB. Peptidyl-prolyl cisltrans isomerase (PPIase) activity of nuclear CypA is inhibited by zinc ions. The zinc inhibited CypA does not bind cyclosporin A (CsA). We suggest that nuclear Cyp in complex with zinc ions recognizes DNA sequences and is involved in transcription modulating processes.

FKBP51, a novel T-cell-specific immunophilin capable of calcineurin inhibition

The immunosuppressive drugs FK506 and cyclosporin A block T-lymphocyte proliferation by inhibiting calcineurin, a critical signaling molecule for activation. Multiple intracellular receptors (immunophilins) for these drugs that specifically bind either FK506 and rapamycin (FK506-binding proteins [FKBPs]) or cyclosporin A (cyclophilins) have been identified. We report the cloning and characterization of a new 51-kDa member of the FKBP family from murine T cells. The novel immunophilin, FKBP51, is distinct from the previously isolated and sequenced 52-kDa murine FKBP, demonstrating 53% identity overall. Importantly, Western blot (immunoblot) analysis showed that unlike all other FKBPs characterized to date, FKBP51 expression was largely restricted to T cells. Drug binding to recombinant FKBP51 was demonstrated by inhibition of peptidyl prolyl isomerase activity. As judged from peptidyl prolyl isomerase activity, FKBP51 had a slightly higher affinity for rapamycin than for FK520, an FK506 analog. FKBP51, when complexed with FK520, was capable of inhibiting calcineurin phosphatase activity in an in vitro assay system. Inhibition of calcineurin phosphatase activity has been implicated both in the mechanism of immunosuppression and in the observed toxic side effects of FK506 in nonlymphoid cells. Identification of a new FKBP that can mediate calcineurin inhibition and is restricted in its expression to T cells suggests that new immunosuppressive drugs may be identified that, by virtue of their specific interaction with FKBP51, would be targeted in their site of action.

Cloning and characterization of a Plasmodium falciparum cyclophilin gene that is stage-specifically expressed

An immunosuppressive agent, cyclosporin A (CsA), has antimalarial activity in several Plasmodium species. Cyclophilins of several species including Plasmodium falciparum exhibit peptidyl-prolyl cis-trans isomerase activity which is inhibited by CsA. A gene encoding P. falciparum cyclophilin (PFCyP) was cloned and characterized. This gene has the entire coding sequence for the mature protein plus a 39-amino-acid-long N-terminal extension. Most of the amino acids predicted to be involved in the peptidyl-prolyl cis-trans isomerase activity and CsA binding are present in the cloned gene. The PFCyP also has the single highly conserved tryptophan residue that is a major determinant in the inhibition of PPIase activity by CsA. The PFCyP coding sequence with or without the N-terminal amino-acid extension was used to construct recombinant expression vectors which were transformed into E. coli. Both vectors produced enzymatically active mature PFCyP proteins that were sensitive to CsA. Northern blot analysis of RNA isolated from the synchronized parasite cultures verified the expression of PFCyP in all erythrocytic stages of the parasite, but at variable levels. The highest level of expression was observed in ring-stage parasites, a stage shown to be more susceptible to CsA. Inhibition of P. falciparum growth in vitro by CsA was re-evaluated for chloroquine-sensitive and chloroquine-resistant strains of the parasite. Essentially, there was no difference between the two strains for the concentration of CsA required to yield 50% inhibition in 48 h of exposure (0.25-0.4 microM).

Secretion by Trypanosoma cruzi of a peptidyl-prolyl cis-trans isomerase involved in cell infection

Macrophage infectivity potentiators are membrane proteins described as virulence factors in bacterial intracellular parasites, such as Legionella and Chlamydia. These factors share amino acid homology to eukaryotic peptidyl-prolyl cis-trans isomerases that are inhibited by FK506, an inhibitor of signal transduction in mammalian cells with potent immunosuppressor activity. We report here the characterization of a protein released into the culture medium by the infective stage of the protozoan intracellular parasite Trypanosoma cruzi. The protein possesses a peptidyl-prolyl cis-trans isomerase activity that is inhibited by FK506 and its non-immunosuppressing derivative L-685,818. The corresponding gene presents sequence homology with bacterial macrophage infectivity potentiators. The addition of the protein, produced heterologously in Escherichia coli, to cultures of trypomastigotes and simian epithelial or HeLa cells enhances invasion of the mammalian cells by the parasites. Antibodies raised in mice against the T.cruzi isomerase greatly reduce infectivity. A similar reduction of infectivity is obtained by addition to the cultures of FK506 and L-685,818. We concluded that the T.cruzi isomerase is involved in cell invasion.

Biochemical and calmodulin binding properties of estrogen receptor binding cyclophilin expressed in Escherichia coli

Bovine estrogen receptor binding cyclophilin (ERBC), a cyclophilin component of the unactivated estrogen receptor, has been efficiently expressed in Escherichia coli as a fusion with glutathione S-transferase (GST) and purified by single-step chromatography on glutathione-agarose. Thrombin cleavage from GST allowed the isolation of purified, recombinant ERBC. The fusion protein, GST-ERBC, and recombinant ERBC were both characterised for peptidyl prolyl cis-trans isomerase activity. With N-succinyl-Ala-Ala-Pro-Phe-p-nitroanilide as substrate, GST-ERBC demonstrated a kcat/KM value of 5.1 x 10(5) M-1s-1 at 5 degrees C. The isomerase activity was inhibited by cyclosporin A with an IC50 value of 1030 nM. These values indicate that ERBC has a decreased catalytic efficiency and sensitivity to cyclosporin A relative to human cyclophilin. Retention of the GST-ERBC fusion protein on calmodulin-agarose in the presence of Ca2+ and subsequent elution with EGTA has provided evidence that ERBC is a calmodulin-binding protein.

Time-dependent inhibition of peptidylprolyl cis-trans-isomerases by FK506 is probably due to cis-trans isomerization of the inhibitor's imide bond

Free in solution, the immunosuppressive compounds cyclosporin A (CsA), FK506, ascomycin and rapamycin are present in many solvents in various slowly interconverting conformations. Together with their cellular receptor proteins, cyclophilin (CyP) and FK506-binding protein (FKBP), however, these inhibitors have been shown to have a homogeneous conformation. The existence of a slow cis-trans interconversion of an imidic bond in the inhibitor molecule during the course of the formation of the CsA-CyP18cy complex (where CyP18cy is human 18 kDa cytosolic CyP) prompted us to investigate the reaction of the peptidomacrolides FK506, ascomycin and rapamycin with two specific binding-proteins in more detail. Since formation of the FK506-FKBP complex results in the inhibition of the peptidylprolyl cis-trans-isomerase activity of the binding protein, we used the enzyme's decrease in enzymic activity to monitor binding of the inhibitors to their enzyme targets. For FK506, the kinetics of inhibition of human 12 kDa cytosolic FKBP (FKBP12cy) were clearly dependent on time. Subsequent to a rapid inactivation reaction, not resolved in its kinetics due to manual mixing, a slow dominant first-order inactivation process with a relaxation time of 1163 s at 10 degrees C was observed. Concomitantly the Ki value of the slow phase dropped 2.6-fold within the first 60 min of incubation. Using the FKBP12cy homologue 25 kDa membrane FKBP (FKBP25mem), a bacterial peptidylprolyl cis-trans-isomerase, the rate and amplitudes of the inhibition reactions were very similar to FKBP12cy. On the other hand, the kinetics and amplitudes of the inhibition of FKBP12cy varied significantly if rapamycin was used as an inhibitor instead of FK 506. Owing to reduced conformation transition in rapamycin upon binding to FKBP12cy, the slow phase during inhibition was significantly decreased in amplitude. A likely reason for this became apparent when the activation-enthalpy and the pH-dependence of the rate constants of the slow phase were determined. We conclude that the cis to trans interconversion of the pipecolinyl bond of the three peptidomacrolides may be responsible for the slow process. There was no indication of a suicide catalysis of this process by FKBPs.

Effects of immunosuppressive peptidyl-prolyl cis-trans isomerase (PPIase) inhibitors, cyclosporin A, FK506, ascomycin and rapamycin, on hair growth initiation in mouse: immunosuppression is not required for new hair growth

The effects of immunosuppressive peptidyl-prolyl cis-trans isomerase (PPIase) inhibitors, cyclosporin A, FK506, ascomycin and rapamycin, on hair growth initiation (anagen hair induction) in mouse were studied by topical application on the dorsal skin surface during the telogen phase of the hair cycle. Single applications of cyclosporin A and FK506 (10 to 100 nmol in 5 microliters of ethanol) induced new hair growth in 12 days within the restricted area where the compounds were applied. On the other hand, ascomycin and rapamycin did not initiate new anagen hairs even at higher doses (1 mumol in 5 to 10 microliters of ethanol). The effects of simultaneous application of the immunosuppressants were also tested by a single topical application. Ascomycin did not inhibit the anagen hair induction by cyclosporin A, but inhibited hair induction by FK506. Rapamycin inhibited new hair growth induced by cyclosporin A and FK506. These results suggest that the inhibition of PPIase is not required for the initiation of a new hair cycle in mice, and that anagen hair induction caused by cyclosporin A and FK506 is not a result of immunosuppression. The present results also indicate that a single application of an adequate quantity of cyclosporin A and FK506 is sufficient to initiate new hair growth.