Peptidyl-prolyl Cis Research Articles

FK506-binding protein of the hyperthermophilic archaeum, Thermococcus sp. KS-1, a cold-shock-inducible peptidyl-prolyl cis–trans isomerase with activities to trap and refold denatured proteins

The FK506 (tacrolimus)-binding protein (FKBP) type peptidyl-prolyl cis–trans isomerase (PPIase) in the hyperthermophilic archaeum Thermococcus sp. KS-1 was shown to be induced by temperature downshift to growth temperatures lower than the optimum. This PPIase (TcFKBP18) showed chaperone-like protein refolding activity in addition to PPIase activity in vitro. It refolded unfolded citrate synthase (CS) and increased the yield of the refolded protein. At a molar ratio of 15:1 ([TcFKBP18] to [CS]) in the refolding mixture, the recovered yield of folded CS was maximal at 62%, whereas that of spontaneous refolding was 11%. Increasing FKBP above a 15:1 ratio decreased the final yield, whereas the aggregation of unfolded CS was suppressed. A cross-linking analysis showed the formation of a complex between TcFKBP18 and unfolded CS (1:1 complex) at molar ratios of 3:1 to 15:1. However, molar ratios of 15:1 or 60:1 induced the binding of multiple FKBP molecules to an unfolded CS molecule (multimeric complex). Disrupting hydrophobic interaction by adding ethylene glycol at a molar ratio of 60:1 ([TcFKBP18] to [CS]) suppressed the formation of this multimeric complex, simultaneously enhancing CS refolding. FK506 also suppressed the formation of the multimeric complex while increasing the chaperone-like activity. These results suggest that the hydrophobic region of TcFKBP18, probably the FK506-binding pocket, was important for the interaction with unfolded proteins. No cross-linked product was detected between TcFKBP18 and native dimeric CS. TcFKBP18 probably traps the unfolded protein, then refolds and releases it in a native form. This FKBP might be important at growth temperatures lower than the optimum in Thermococcus sp. KS-1 cells.

FK506-binding protein of the hyperthermophilic archaeum, Thermococcus sp. KS-1, a cold-shock-inducible peptidyl-prolyl cis-trans isomerase with activities to trap and refold denatured proteins.

The FK506 (tacrolimus)-binding protein (FKBP) type peptidyl-prolyl cis-trans isomerase (PPIase) in the hyperthermophilic archaeum Thermococcus sp. KS-1 was shown to be induced by temperature downshift to growth temperatures lower than the optimum. This PPIase (TcFKBP18) showed chaperone-like protein refolding activity in addition to PPIase activity in vitro. It refolded unfolded citrate synthase (CS) and increased the yield of the refolded protein. At a molar ratio of 15:1 ([TcFKBP18] to [CS]) in the refolding mixture, the recovered yield of folded CS was maximal at 62%, whereas that of spontaneous refolding was 11%. Increasing FKBP above a 15:1 ratio decreased the final yield, whereas the aggregation of unfolded CS was suppressed. A cross-linking analysis showed the formation of a complex between TcFKBP18 and unfolded CS (1:1 complex) at molar ratios of 3:1 to 15:1. However, molar ratios of 15:1 or 60:1 induced the binding of multiple FKBP molecules to an unfolded CS molecule (multimeric complex). Disrupting hydrophobic interaction by adding ethylene glycol at a molar ratio of 60:1 ([TcFKBP18] to [CS]) suppressed the formation of this multimeric complex, simultaneously enhancing CS refolding. FK506 also suppressed the formation of the multimeric complex while increasing the chaperone-like activity. These results suggest that the hydrophobic region of TcFKBP18, probably the FK506-binding pocket, was important for the interaction with unfolded proteins. No cross-linked product was detected between TcFKBP18 and native dimeric CS. TcFKBP18 probably traps the unfolded protein, then refolds and releases it in a native form. This FKBP might be important at growth temperatures lower than the optimum in Thermococcus sp. KS-1 cells.

Characterisation of a cyclophilin isoform in Trypanosoma cruzi

The immunosuppressive drug cyclosporin A (CsA) has shown antiparasitic activity against several protozoans and helminths, when complexed to proteins called cyclophilins (CyPs). In this paper, the molecular characterisation of one member of the CyP family in Trypanosoma cruzi is reported. TcCyP19 gene proved to be highly conserved compared to CyPs from other organisms and was highly homologous to a Trypanosoma brucei brucei CyPA. This gene was expressed in Escherichia coli and the purified recombinant protein exhibited a peptidyl prolyl cis- trans isomerase activity that was inhibited by CsA (IC 50=18.4±0.8 nM). The TcCyP19 gene was located on two chromosomal bands in T. cruzi CL Brener clone.

Binding and regulation of the transcription factor NFAT by the peptidyl prolyl cis– trans isomerase Pin1

Nuclear factor of activated T cells (NFAT) plays a key role in T cell activation. The activation of NFAT involves calcium- and calcineurin-dependent dephosphorylation and nuclear translocation from the cytoplasm, a process that is opposed by protein kinases. We show here that the peptidyl prolyl cis– trans isomerase Pin1 interacts specifically with the phosphorylated form of NFAT. The NFAT–Pin1 interaction is mediated through the WW domain of Pin1 and the serine–proline-rich domains of NFAT. Furthermore, binding of Pin1 to NFAT inhibits the calcineurin-mediated dephosphorylation of NFAT in vitro, and overexpression of Pin1 in T cells inhibits calcium-dependent activation of NFAT in vivo. These results suggest a possible role for Pin1 in the regulation of NFAT in T cells.

Receptor accessory folding helper enzymes: the functional role of peptidyl prolyl cis/ trans isomerases

Receptor accessory peptidyl prolyl cis/ trans isomerases (PPIases) of the FKBP and cyclophilin types form receptor heterocomplexes with different stabilities. PPIases have been found to associate with other receptor heterocomplex constituents via either proline-directed active sites or additional domains of the enzymes. The single-domain PPIases FKBP12 and FKBP12.6 are shown to interact with receptor protein kinases and calcium channels at their active sites. In contrast, heterooligomeric nuclear receptors contain multi-domain PPIases like FKBP51, FKBP52 or cyclophilin 40 that directly interact with the chaperone hsp90 via the tetratricopeptide repeat modules of the folding helper enzymes. PPIases play a critical role in the functional arrangement of components within receptor heterocomplexes.

Molecular characterization of TgMIC5, a proteolytically processed antigen secreted from the micronemes of Toxoplasma gondii

During invasion of host cells, Toxoplasma gondii discharges the contents of small, apically located secretory organelles called micronemes. Micronemal proteins are known to be necessary for both parasite motility and invasion of host cells. To further define the contents of Toxoplasma micronemes, we used cell fractionation and secretion-modulating drugs to identify six novel, putative micronemal proteins. In this paper we describe preliminary characterization of one of these novel proteins, TgMIC5. Molecular cloning and DNA sequence analysis of the TgMIC5 cDNA and gene revealed that it encodes a previously identified immunodominant antigen called H4. TgMIC5 also possesses a consensus sequence unique to members of the parvulin family of peptidyl–prolyl cis–trans isomerases (PPIases). TgMIC5 is expressed as a preproprotein, which is proteolytically processed to a proprotein by signal peptidase before being further processed to a mature protein of 22 kDa. Using a combination of protein secretion experiments, immunofluorescence and immunoelectron microscopy, we demonstrated that TgMIC2 is stored in the micronemes of T. gondii tachyzoites before it is secreted into the surrounding medium. Based on its homology with parvulin-like PPIases, TgMIC5 may assist in the folding of other micronemal proteins that function in invasion of host cells by T. gondii tachyzoites.

Post-translational reduction of cell surface expression of insulin receptors by cyclosporin A, FK506 and rapamycin in bovine adrenal chromaffin cells

Long-term (≥3 h) treatment of cultured bovine adrenal chromaffin cells with cyclosporin A (CsA) decreased cell surface 125I-insulin binding by 62% in a concentration (IC 50=18 μM)- and time ( t 1/2=16 h)-dependent manner, but did not change the K d value. FK506 (1 μM) or rapamycin (3 μM) treatment reduced 125I-insulin binding. Western blot analysis showed that CsA treatment decreased insulin receptor (IR) β-subunit level ( t 1/2=15 h) in membrane fraction, but did not alter total cellular levels of IR precursor and IR β-subunit. Internalization rate of cell surface IR measured by using brefeldin A, an inhibitor of vesicular exit from the trans-Golgi network, was comparable between non-treated and CsA-treated cells. Thus, CsA, FK506 and rapamycin inhibit peptidyl prolyl cis- trans isomerase activities of cyclophilin and FK506-binding protein, and down-regulate IR presumably by reducing cell surface externalization of IR.

FK506-binding protein-type peptidyl-prolyl cis– trans isomerase from a halophilic archaeum, Halobacterium cutirubrum

The halophilic archaeum, Halobacterium cutirubrum, has been shown to have a cyclophilin-type peptidyl-prolyl cis– trans isomerase (PPIase). Because most archaeal genomes studied only have genes for FK506-binding proteins (FKBPs) as a PPIase, it has been unclear whether H. cutirubrum has an FKBP-type PPIase or not. In the present study, a gene encoding an FKBP-type PPIase was cloned from genomic DNA of H. cutirubrum and then sequenced. This FKBP was deduced to be composed of 303 amino acid residues with a molecular mass of 33.3 kDa. Alignment of its amino acid sequence with those of other reported FKBPs showed that it contained two insertion sequences in the regions corresponding to the bulge and flap of human FKBP12, which are common to archaeal FKBPs. Its C-terminal amino acid sequence was approximately 130 amino acids longer than the FKBPs of Methanococcus thermolithotrophicus and Thermococcus sp. KS-1. Among the 14 conserved amino acid residues that form the FK506 binding pocket, only three were found in this FKBP. This gene was expressed as a fusion protein with glutathione S-transferase (GST) in Escherichia coli, and the N-terminal GST portion was removed by protease digestion. The purified recombinant FKBP showed a weak PPIase activity with a low sensitivity to FK506. This FKBP suppressed aggregation of the unfolded protein.

Expression of a Solanum tuberosum cyclophilin gene is regulated by fungal infection and abiotic stress conditions

Cyclophilins (CyPs) are ubiquitous proteins with an intrinsic enzymatic activity of peptidyl-prolyl cis- trans isomerase that catalyzes the rotation of X-Pro peptide bonds. These enzymes are believed to play a role in the folding of certain proteins. In addition, CyPs might be important in signal transduction processes. A cDNA library was prepared from potato ( Solanum tuberosusm) tubers infected with the fungus Fusarium solani f. sp eumartii. Using a PCR-amplified subtracted cDNA probe, a clone encoding a cytosolic form of CyP, called StCyP ( S̱ olanum ṯ uberosum CyP), was isolated. Except in tubers, StCyP is expressed at high levels in tissues of healthy potato plants. Northern blot analyses revealed that both wounding and fungal infection increased the level of StCyP mRNA in tubers. However, whereas wounding causes a transient accumulation of StCyP mRNA, fungal infection results in a maintained accumulation of this transcript. StCyP mRNA accumulation is also stimulated by the application of absicic acid (ABA) and methyl jasmonate (MeJA) in tubers. Treatment with fungal elicitor or salicilic acid (SA) has no effect on the level of StCyP mRNA accumulation. Together these results indicate that the observed accumulation of StCyP mRNAs in fungal-infected potato tubers might be a response to the wound produced by the penetration and colonization of the tissue by the pathogen. Furthermore, accumulation of StCyP transcripts was also detected when the potato tubers were exposed to heat-shock treatment. These findings support a role for cyclophilins in the plant response to environmental stresses.

Three-step chromatographic purification of Cpr6, a cyclophilin from Saccharomyces cerevisiae

Cyclophilins constitute a group of peptidyl-prolyl cis–trans isomerases (PPIs), known to be involved in protein folding. Because of their ability to bind the immunosuppresant drug Cyclosporin A (CsA), they are also called immunophilins. Immunophilins, which exhibit a relative molecular mass higher than 40 000, are further found in complex with Hsp90, a major cytosolic molecular chaperone. The present work describes a three-step chromatographic purification of recombinant Cpr6, a cyclophilin from Saccharomyces cerevisiae. The cDNA of Cpr6 was cloned into a pRSET A-plasmid with an N-terminal 6 x histidine-tag (his-tag) and transformed into the BL21[DE3]pLysS strain. After collection of the bacterial material and lysis of the cells the cell lysate was centrifuged and loaded onto a metal chelating column. After extensive washing the protein was eluted with a step gradient from 20 to 250 mM imidazol. The pooled protein was dialysed against ethylenedinitrilo tetraacetic acid (EDTA)–buffer, and loaded onto a strong anion-exchanger. Cpr6 containing fractions were then, in a last step, loaded onto a gel permeation chromatography column. The purity of the resulting protein was measured by silver stained sodium dodecyl sulphate–polyacrylamide gel electrophoresis (SDS–PAGE) and, additionally, as Cpr6 does not contain tryptophan residues by tryptophan residue titration. Based on a standard curve the content of contaminating tryptophan residues in the purified protein solution was determined. A typical yield of 1 mg pure protein per g of wet cells was achieved with the described procedure.

Biochemical analysis of mouse FKBP60, a novel member of the FKPB family

We have identified mouse and human FKBP60, a new member of the FKBP gene family. FKBP60 shares strongest homology with FKBP65 and SMAP. FKBP60 contains a hydrophobic signal peptide at the N-terminus, 4 peptidyl-prolyl cis/ trans isomerase (PPIase) domains and an endoplasmic reticulum retention motif (HDEL) at the C-terminus. Immunodetection of HA-tagged FKBP60 in NIH-3T3 cells suggests that FKBP60 is segregated to the endoplasmic reticulum. Northern blot analysis shows that FKBP60 is predominantly expressed in heart, skeletal muscle, lung, liver and kidney. With N-succinyl-Ala-Ala-Pro-Phe- p-nitroanilide as a substrate, recombinant GST-FKBP60 is shown to accelerate effectively the isomerization of the peptidyl-prolyl bond. This isomerization activity is inhibited by FK506. mFKBP60 binds Ca 2+ in vitro, presumably by its C-terminal EF-hand Ca 2+ binding motif, and is phosphorylated in vivo. hFKBP60 has been mapped to 7p12 and/or 7p14 by fluorescence in situ hybridization (FISH).

Identification and characterization of a 14 kDa human protein as a novel parvulin-like peptidyl prolyl cis/ trans isomerase

A second member of the parvulin family of peptidyl-prolyl cis/ trans isomerases was identified in a human lung cDNA library. The gene encoded a protein named hPar14 that has 131 amino acid residues and a molecular mass of 13 676 Da. Sequence comparison showed 34.5% identity to E. coli Par10 and 34% identity to human Pin1 ( hPar18) within a C-terminal region of 87 or 120 amino acid residues, respectively. In comparison to the E. coli Par10, hPar14 possesses a N-terminal extension of 41 amino acid residues. This extension does not contain a polyproline II helix-binding motif typical of the known eukaryotic parvulins. The hPar14 does not accelerate the cis to trans interconversion of oligopeptides with side chain-phosphorylated Ser(Thr)-Pro moieties as hPin1 did. In contrast, it showed preference of an arginine residue adjacent N-terminal to proline. Northern blot analysis revealed expression of the gene within various human tissues like heart, placenta, liver, kidney and pancreas.

Multiple unfolded states of UDP-galactose 4-epimerase from yeast Kluyveromyces fragilis : Involvement of proline cis– trans isomerization in reactivation

UDP-galactose 4-epimerase from yeast Kluyveromyces fragilis is a dimeric molecule of 75 kDa per subunit with one molecule of cofactor NAD per dimer. It undergoes unfolding and complete dissociation in presence of 8 M urea at pH 7.0 by 10 min. It can be functionally reconstituted almost quantitatively in 2 h by dilution with 20 mM sodium phosphate buffer, pH 7 containing 1 mM extraneous NAD under a second order kinetics [Bhattacharyya, D. (1993) Biochemistry 32, 9726–9734]. Denaturation between 10–60 min inversely affects both the rate and maximum recovery of activity upon refolding. Aggregation of this protein has not been observed under these conditions. The time dependent reaction at the unfolded state is independent of pH between 5.4–10.4 but strongly dependent on temperature of denaturation between 0–20°C. Unfolding at 0°C divides the protein largely into two populations – 34% of fast folding species following an apparent first order kinetics and 59% of slow folding species following a second order kinetics of reactivation. A very fast folding species of low abundance 3.5–7.5% depending on temperature of denaturation has been identified, which gets active status within the dead time of mixing. Interaction with the active site directed fluorescence probe 1-anilino 8-naphthalene sulfonic acid (1-ANS) and estimation of bound NAD suggest that the catalytic region of this enzyme is not formed in the long term denatured samples. The whole process of reactivation is catalysed by peptidyl prolyl cis– trans isomerase and thus suggests that one or more proline residues stereochemically control the rate limiting step of reactivation.

Effect of prolyl isomerase on the folding reactions of staphylococcal nuclease.

The low-temperature fluorescence-detected refolding of staphylococcal nuclease (SNase) can be described by three slow kinetic phases. The slowest phase is absent in the P117G mutant of SNase. Peptidyl prolyl cis-trans isomerase (cyclophilin), which has been shown to catalyze the slow folding reactions of some proteins, was employed to determine which of the refolding reactions of SNase and P117G SNase involve proline isomerization. We report here that all three folding phases of the wild type and the slower phase of P117G SNase are catalyzed by prolyl isomerase, indicating that proline isomerization is involved in these fluorescence-detected phases in the refolding of SNase. Since the rates of these phases are denaturant-dependent, we conclude that the slow folding steps involve isomerization of non-native cis proline peptide bonds and are tightly coupled to denaturant-sensitive structural changes.

Domain movement in rabbit muscle adenylate kinase might involve proline isomerization

The fluorescence probe, 8-anilino-1-naphthalenesulfonic acid (ANS), was used to monitor the induced-fit conformational movement in rabbit muscle adenylate kinase. In 50 mM Tris-HCl buffer (pH 8.1), the time course of ANS binding to rabbit muscle adenylate kinase is a biphasic process. The fast phase completes within the dead-time of the stopped-flow equipment used (about 15 ms), while the slow phase ends in about 10 minutes. In the presence of 2.0 μM peptidyl prolyl cis/ trans-isomerase, the rate constant of the slow phase reaction is accelerated about 2.4-fold, suggesting that the domain movement during ANS binding to rabbit muscle adenylate kinase may involve proline isomerization. The activation energy of the slow phase was determined to be 74.6 kJ/mol, which is comparable to the activation energy of proline cis/ trans-isomerization (about 80 kJ/mol).

A serine/arginine-rich nuclear matrix cyclophilin interacts with the C-terminal domain of RNA polymerase II.

The largest subunit of RNA polymerase II shows a striking difference in the degree of phosphorylation, depending on its functional state: initiating and elongating polymerases are unphosphorylated and highly phosphorylated respectively. Phosphorylation mostly occurs at the C-terminal domain (CTD), which consists of a repetitive heptapeptide structure. Using the yeast two-hybrid system, we have selected for mammalian proteins that interact with the phosphorylated CTD of mammalian RNA polymerase II. A prominent isolate, designated SRcyp/CASP10, specifically interacts with the CTD not only in vivo but also in vitro . It contains a serine/arginine-rich (SR) domain, similar to that found in the SR protein family of pre-mRNA splicing factors, which is required for interaction with the CTD. Most remarkably, the N-terminal region of SRcyp includes a peptidyl-prolyl cis - trans isomerase domain characteristic of immunophilins/cyclophilins (Cyp), a protein family implicated in protein folding, assembly and transport. SRcyp is a nuclear protein with a characteristic distribution in large irregularly shaped nuclear speckles and co-localizes perfectly with the SR domain-containing splicing factor SC35. Recent independent investigations have provided complementary data, such as an association of the phosphorylated form of RNA polymerase II with the nuclear speckles, impaired splicing in a CTD deletion background and inhibition of in vitro splicing by CTD peptides. Taken together, these data indicate that factors directly or indirectly involved in splicing are associated with the elongating RNA polymerases, from where they might translocate to the nascent transcripts to ensure efficient splicing, concomitant with transcription.

Presence of cyclophilin A in synovial fluids of patients with rheumatoid arthritis.

Cyclophilins have been suggested to act as leukocyte chemotactic factors produced in the course of inflammation. Therefore we looked for the presence of cyclophilins in the synovial fluids (SF) from patients with rheumatoid arthritis (RA). Peptidyl prolyl cis-trans isomerase activity (PPIase) was measured in SF from knee punctures of 26 patients with RA and five patients with knee osteoarthritis (OA). PPIase was detected in SF from RA patients, but not in samples from OA patients. Enzyme activity was sensitive to inhibition by cyclosporin A (IC50 = 28-50 nM). Estimated concentrations of the SF-derived cyclophilin based on the enzyme activity were in the range of 11 to 705 nM. The presence of cyclophilin in the SF showed disease correlation; its concentration correlated with the number of cells in the SF (r = 0.91, P < 0.0001) and with the percentage of neutrophils in the cellular infiltrate and was higher in more acute cases of joint swelling. In immunoblots of partially purified preparations of SF from RA patients, an approximately 18-kD protein band reacted with polyclonal antibodies that recognize cyclophilin A and B, but not with antibodies specific for cyclophilin B. Sequencing of this protein revealed identity of the NH2-terminal amino acids with those of human cyclophilin A. The finding is unexpected since cyclophilin B rather than A is generally regarded as the secreted isoform, the presence of cyclophilin A being confined to the cytoplasm. Our data support the hypothesis that cyclophilins may contribute to the pathogenesis of inflammatory diseases, possibly by acting as cytokines. This may offer a possible explanation of the effectiveness of cyclosporin A in RA, in addition to the known immunosuppressive effects of the drug.

Cloning and biochemical characterization of the cyclophilin homologues from the free-living nematode Caenorhabditis elegans

Cyclosporin A (CsA) is the most widely used immunosuppressive agent, whose properties are exerted via an interaction with cyclophilin, resulting in down-regulation of signal-transduction events in the T-cell. Cyclophilin is identical with peptidylprolyl cis-trans isomerase (PPI; EC 5.2.1.8), an enzyme which catalyses the isomerization between the two proline conformations in proteins, thereby acting as a catalyst in protein-folding events. Several reports indicate that CsA has potent anti-parasitic activity, effective against both protozoan and helminth species. In order to understand the various biological roles that cyclophilins play we have initiated a study of these proteins in the genetically tractable nematode Caenorhabditis elegans. Here we describe the cloning and characterization of 11 cyclophilin genes (cyp-1 to -11) derived from this nematode; this is currently the greatest number of isoforms described in a single species. Southern blotting and physical mapping indicated that these genes are dispersed throughout the nematode genome. A high degree of conservation exists between several isoforms, which also share characteristics with the ubiquitous isoforms previously described. The remaining isoforms are divergent, having altered CsA-binding domains and additional non-cyclophilin domains, which may impart compartmental specificity. Ten of these isoforms have been expressed in Escherichia coli, and the resultant fusion proteins have been examined biochemically for PPI activity, which they all possess. Isomerase activity is highest in the conserved and lowest in divergent isoforms, perhaps indicating a more specific substrate for the latter. Analysis of the C. elegans cyp genes will provide answers as to the roles played by cyclophilins in protein folding and signal transduction.

Overexpression of p59-HBI (FKBP59), Full Length and Domains, and Characterization of PPlase Activity

It has been previously proposed that the rabbit p59-HBI ( H eat shock protein B inding I mmunophilin) or rFKBP59 ( FK 506 B inding P rotein), found associated with the 90 kDa heat shock protein in nontransformed steroid receptor complexes, has three domains structurally related to hFKBP12 (Callebaut, I., Renoir, J.M., Lebeau, MC., Massol, N., Burny, A., Baulieu, E.E. and Mornon, J.P. (1992) Proc. Natl. Acad. Sci., USA 89, 6270-6274). Here we report the overexpression, as fusion proteins in E. coli, of the full length p59-HBI and a series of p59-HBI mutants delimiting these domains and their respective peptidyl prolyl cis trans isomerase (PPlase) activity. The PPlase activity of p59-HBI is comparable to that of hFKBP12 and is due to domain p59-HBI I which displays the highest homology with this immunophilin. The residual enzymatic activity found in domain p59-HBI II is discussed.

The cis/ trans interconversion of the calcium regulating hormone calcitonin is catalyzed by cyclophilin

The cytosolic peptidyl-prolyl cis/ trans isomerase cyclophilin from pig kidney can accelerate catalytically the cis/ trans isomerization of prolyl peptide bonds. One- and two-dimensional 1H NMR spectroscopy was used to prove that the polypeptide hormone calcitonin is a substrate for cyclophilin. Isomerization of only one of the two prolyl peptide bonds is catalyzed significantly. The efficiency of catalysis was calculated by lineshape analysis and NOESY spectroscopy. Cyclosporin A completely blocks the effect of the enzyme on the conformational dynamics of the polypeptide.