1-Anilino-8-naphthalene sulfonate (ANS) is not a desirable probe for determining the molten globule state of chymopapain

The molten globule (MG) state of proteins is widely detected through binding with 1-anilino-8-naphthalene sulphonate (ANS), a fluorescent dye. This strategy is based upon the assumption that when in molten globule state, the exposed hydrophobic clusters of protein are readily bound by the nonpolar anilino-naphthalene moiety of ANS molecules which then produce brilliant fluorescence. In this work, we explored the acid-induced unfolding pathway of chymopapain, a cysteine proteases from Carica papaya, by monitoring the conformational changes over a pH range 1.0–7.4 by circular dichroism, intrinsic fluorescence, ANS binding, acrylamide quenching, isothermal titration calorimetry (ITC) and dynamic light scattering (DLS). The spectroscopic measurements showed that although maximum ANS fluorescence intensity was observed at pH 1.0, however protein exhibited ∼80% loss of secondary structure which does not comply with the characteristics of a typical MG-state. In contrast at pH 1.5, chymopapain retains substantial amount of secondary structure, disrupted side chain interactions, increased hydrodynamic radii and nearly 30-fold increase in ANS fluorescence with respect to the native state, indicating that MG-state exists at pH 1.5 and not at pH 1.0. ITC measurements revealed that ANS molecules bound to chymopapain via hydrophobic interaction were more at pH 1.5 than at pH 1.0. However, a large number of ANS molecules were also involved in electrostatic interaction with protein at pH 1.0 which, together with hydrophobically interacted molecules, may be responsible for maximum ANS fluorescence. We conclude that maximum ANS-fluorescence alone may not be the criteria for determining the MG of chymopapain. Hence a comprehensive structural analysis of the intermediate is essentially required.

The catalytic mode of cysteine proteinases of papain (C1) family

The Proton Inventory (PI) method has been applied in the hydrolysis of synthetic substrates by papain, chymopapain and stem bromelain, comparing also their corresponding pH-(k(cat)/K(m)) profiles, and it was found: (a) k(cat)/K(m)=k(1), and thus K(S)=k(2)/k(1) is a dynamic equilibrium constant, (b) bowed-downward PI for k(cat)/K(m) exhibiting large inverse SIE, and (c) linear PI exhibiting large normal SIE for K(S), k(2) and k(3). A novel finding of this work is that the association of substrates onto all three studied cysteine proteinases proceeds via a stepwise pathway, in contrast to purely concerted pathways found previously for both acylation and deacylation. A hydrogen bond, which seems more likely to be developed across a pK(a)-value close to 4.00, connecting [see text] (papain/chymopapain or bromelain numbering), constitutes another novelty of this work.

Effect of Polyethylene Glycols on the Function and Structure of Thiol Proteases

Thiol proteases are industrially significant proteins with catalytic efficiency. The effect of low, medium and high molecular-weight poly (ethylene glycol) (PEG- 400, 6000 and 20000) on the stability of thiol proteases (papain, bromelain and chymopapain) has been studied by activity measurements using synthetic substrate. Structural studies performed on papain by far UV circular dichroism spectroscopic measurements indicate that there is loss in secondary structure of the protein in presence of increasing concentration of PEGs. Intrinsic fluorescence measurements lead us to conclude that tryptophan residues of protein encounter non-polar microenvironment in presence of PEG solvent while acrylamide quenching shows greater accessibility of tryptophan residues of papain in presence of PEGs. Extrinsic fluorescence measurements lead us to conclude that PEGs bind to the hydrophobic sites on the protein and thus destabilize it. Thermal denaturation studies show that melting temperature of papain is decreased in presence of PEGs. Possible mechanism of destabilization is discussed next. The results imply that caution must be exercised in the use of PEGs with thiol proteases or hydrophobic proteins in general, for different industrial applications, even at room temperature.

Hofmeister effects in protein unfolding kinetics: Estimation of changes in surface area upon formation of the transition state

We studied the effect of three electrolytes (LiCl, Na(2)SO(4), GuHCl) on the unfolding reaction of chymopapain, a two-domain protein belonging in the papain family of cysteine proteinases. Due to methodological reasons, these studies were carried out at pH 1.5 where the protein unfolds following biphasic kinetics. We have observed the presence of two different effects of electrolyte concentration on the unfolding reactions. At low ionic strength, the ionic atmosphere brought about an increase in reaction rates, regardless of the type of ions being present; this effect is attributed to a general "electrostatic screening" of charge-charge interactions in the macromolecule. At high ionic strength, each electrolyte exerted a distinctively different effect: both rate constants were largely increased by GuHCl (a well-known protein denaturant), but only slightly by LiCl; in contrast, Na(2)SO(4) (a good precipitant) decreased the value of both unfolding rates. These ion-specific (Hofmeister) effects were further used to estimate changes in accessible surface area (DeltaASA) upon formation of the transition states (TS) for unfolding. Results obtained with LiCl and Na(2)SO(4), which we analyzed by means of a parameterization derived from published solubility data of amino acid derivatives, are consistent with DeltaASA increments (for each phase) of about 8.0% of the total theoretical DeltaASA for complete unfolding of the chymopapain molecule. Results in the presence of GuHCl, which were analyzed by using a previous parameterization of protein unfolding data, gave larger DeltaASAs of activation, equivalent to 13 and 16% of the total unfolding DeltaASA.

[Chemical modification of chymopapain with monomethoxypolyethylene glycol and its effect on enzymic activity and antigenicity]

OBJECTIVE

To study the effect of chemical modification of chymopapain with monomethoxypolyethylene glycol on enzymic activity and antigenicity.

METHODS

Under the substrate protecting and non-substrate protecting, the chymopapain (Cp) was modified with two types of mPEG derivatives mPEG1 and mPEG2. The average ratio of modified-NH2 was tested by trinitrobenzenesulfonic acid (TNBS) method, the enzymic activity was tested with macromolecular casein and ATEE as substrates, the antigenicity of modified enzyme was determined by ELISA method.

RESULTS

(1) Both mPEG1 and mPEG2 can reduce and eliminate antigenicity of Cp, the mPEG2 was better than mPEG1. (2) The enzymic activities of modified Cp were reduced, the enzymic activities of mPEG1-modified Cp were higher than that of mPEG2-modified Cp (especially macromolecular protein as its substrate). (3) The enzymic activities in present of ATEE were obviously higher than that in absent of substrate.

CONCLUSION

When mPEG1 as the modifier and in present of ATEE, the antigenicity of Cp was completely eliminated, and the enzymic activities were still higher.

Structural characterization of the papaya cysteine proteinases at low pH

Current control of gastrointestinal nematodes relies primarily on the use of synthetic drugs and encounters serious problems of resistance. Oral administration of plant cysteine proteinases, known to be capable of damaging nematode cuticles, has recently been recommended to overcome these problems. This prompted us to examine if plant cysteine proteinases like the four papaya proteinases papain, caricain, chymopapain, and glycine endopeptidase that have been investigated here can survive acidic pH conditions and pepsin degradation. The four papaya proteinases have been found to undergo, at low pH, a conformational transition that instantaneously converts their native forms into molten globules that are quite unstable and rapidly degraded by pepsin. As shown by activity measurements, the denatured state of these proteinases which finally results from acid treatment is completely irreversible. It is concluded that cysteine proteinases from plant origin may require to be protected against both acid denaturation and proteolysis to be effective in the gut after oral administration.

[Preparation and purification of polyclonal antibody against chymopapain]

OBJECTIVE

To prepare and purify polyclonal antibody against chymopapain, and to make a foundation for establishing an immunossay for chymopapain.

METHODS

New Zealand rabbit was immunized with chymopapain. Antiserum was purified by Protein A and analyzed by ELISA.

RESULTS

The titer of the antiserum obtained in this experiment by ELISA was up to 1:380000 and the purity was proved to be high by SDS-PAGE.

Structural Basis of Protein Kinetic Stability: Resistance to Sodium Dodecyl Sulfate Suggests a Central Role for Rigidity and a Bias Toward β-Sheet Structure

The term kinetic stability is used to describe proteins that are trapped in a specific conformation because of an unusually high-unfolding barrier that results in very slow unfolding rates. Motivated by the observation that some proteins are resistant to sodium dodecyl sulfate (SDS)-induced denaturation, an attempt was made to determine whether this property is a result of kinetic stability. We studied many proteins, including a few kinetically stable proteins known to be resistant to SDS. The resistance to SDS-induced denaturation was investigated by comparing the migration on polyacrylamide gels of identical boiled and unboiled protein samples containing SDS. On the basis of the different migration of these samples, eight proteins emerged as being resistant to SDS. The kinetic stability of these proteins was confirmed by their slow unfolding rate upon incubation in guanidine hydrochloride. Further studies showed that these proteins were also extremely resistant to proteolysis by proteinase K, suggesting that a common mechanism may account for their resistance to SDS and proteolytic cleavage. Together, these observations suggest that a rigid protein structure may be the physical basis for kinetic stability and that resistance to SDS may serve as a simple assay for identifying proteins whose native conformations are kinetically trapped. Remarkably, most of the kinetically stable SDS-resistant proteins in this study are oligomeric beta-sheet proteins, suggesting a bias of these types of structures toward kinetic stability.

[The preparation and identification of rabbit's antibody of chymopapain]

Chymopapain, one of the four cysteine proteinases of papaya latex, has milk clotting and proteolytic activity. It is mainly used to treat prolapsed intervertebral discs. This paper introduced the preparation of polyclonal antibody of partially purified chymopapain and the identification of the antibody specificity. The polyclonal antibody provides a basis for the further researches and applications of chymopapain.

Insight to structural subsite recognition in plant thiol protease-inhibitor complexes : understanding the basis of differential inhibition and the role of water

BACKGROUND

This work represents an extensive MD simulation / water-dynamics studies on a series of complexes of inhibitors (leupeptin, E-64, E-64-C, ZPACK) and plant cysteine proteases (actinidin, caricain, chymopapain, calotropin DI) of papain family to understand the various interactions, water binding mode, factors influencing it and the structural basis of differential inhibition.

RESULTS

The tertiary structure of the enzyme-inhibitor complexes were built by visual interactive modeling and energy minimization followed by dynamic simulation of 120 ps in water environment. DASA study with and without the inhibitor revealed the potential subsite residues involved in inhibition. Though the interaction involving main chain atoms are similar, critical inspection of the complexes reveal significant differences in the side chain interactions in S2-P2 and S3-P3 pairs due to sequence differences in the equivalent positions of respective subsites leading to differential inhibition.

CONCLUSION

The key finding of the study is a conserved site of a water molecule near oxyanion hole of the enzyme active site, which is found in all the modeled complexes and in most crystal structures of papain family either native or complexed. Conserved water molecules at the ligand binding sites of these homologous proteins suggest the structural importance of the water, which changes the conventional definition of chemical geometry of inhibitor binding domain, its shape and complimentarity. The water mediated recognition of inhibitor to enzyme subsites (Pn.H2O.Sn) of leupeptin acetyl oxygen to caricain, chymopapain and calotropinDI is an additional information and offer valuable insight to potent inhibitor design.

pH dependence of the activation parameters for chymopapain unfolding: influence of ion pairs on the kinetic stability of proteins

We studied the irreversible thermal denaturation of chymopapain, a papain-related cysteine proteinase. It was found that this process follows simple first-order kinetics under all conditions tested. Rate constants determined by monitoring ellipticity changes at 220 or 279 nm are essentially identical, indicating that denaturation involves global unfolding of the protein. Enthalpies (DeltaH(double dagger)) and entropies (DeltaS(double dagger)) of activation for unfolding were determined at various pH values from the temperature dependence of the rate constant. In the pH range 1.1-3.0, a large variation of both DeltaH(double dagger) and DeltaS(double dagger) was observed. For the few proteins studied so far (lysozyme, trypsin, barnase) it is known that activation parameters for unfolding vary little with pH. It is proposed that this contrasting behavior of chymopapain originates from the numerous ion pairs - especially those with low solvent accessibilities - present in its molecular structure. In contrast, fewer, more exposed ion pairs are present in the other proteins mentioned above. Our results were analyzed in terms of differences in the protonation behavior of carboxylic groups between the transition (TS) and native (N) states of the protein. For this purpose, a model of independently titrating sites was assumed, which explained reasonably well the pH dependence of activation parameters, as well as the protonation properties of native chymopapain. According to these calculations, pK values of carboxyls in TS are shifted 0.6-0.9 units upwards with respect to those in N. In addition, some groups in TS appear to be protonated with unusually large enthalpy changes.

Implication of cell wall constituents in the sensitivity of Kluyveromyces lactis strains to amphotericin B

In Kluyveromyces lactis, the cell wall compositions of Kl (ATCC 96897), a wild sensitive strain, and Klm (ATCC 96896), a strain resistant to amphotericin B (AmB), were shown to be very different, since the walls in the latter were significantly enriched in hexosamine, but had a reduced content in phosphate and amino acid. In both strains, the cell walls limited their sensitivity to this antifungal agent. The absence of cell wall increased the sensitivity of the cells to this polyene by 5 to 10-fold. When the cells were treated with enzymes such as pronase and chitinase in order to change the cell wall structure just before inoculation, the yeasts appeared more resistant to the antibiotic. However, treatments with chymopapain and phospholipase C did not significantly change the sensitivity of the two strains to this agent. Cells treated with acid phosphatase displayed a longer lag phase than the control cells. In addition, when cultured in the presence of AmB, the cells were less sensitive to this agent. The present results reveal that both a change in the ionic charges of the cell wall and an alteration in the cell wall structure modified the sensitivity of these yeast strains to AmB.

Structure of chymopapain at 1.7 A resolution

The X-ray structure of chymopapain, a cysteine proteinase isolated from the latex of the fruits of Carica papaya L., has been determined by molecular replacement methods and refined to a conventional R factor of 0.19 for all observed reflections in the range from 9.5 to 1.7 A resolution. The crystals used in this study contained a unique molecular species of chymopapain with two moles of thiomethyl attached to the two free cysteines per mole of enzyme. A comparison is made with the other known papaya proteinase X-ray structures: papain, caricain, and glycyl endopeptidase. Their backbone conformations are extremely similar except for two loop regions. Both regions are located at the surface of the protein and far away of the active site cleft. In each X-ray structure the same water network was found at the interface between the two domains of the enzyme. A close examination of the active site groove showed that the specificity restrictions dictated by the S2 subsite did not differ significantly among the four proteinases.

Immunoglobulin E antibodies to papaya proteinases and their relevance to chemonucleolysis

STUDY DESIGN

Levels of four papaya cysteine proteinases were determined in Chymodiactin, a pharmaceutical preparation of chymopapain (EC 3.4.22.6) used in chemonucleolysis for the treatment of sciatica. Twelve sera known to contain immunoglobulin E antibodies to Chymodiactin were assayed for immunoglobulin E antibodies to these enzymes.

OBJECTIVES

The goal of the study was to determine what contribution each of the four proteinases makes to the allergic response that occasionally occurs during injection of a damaged intervertebral disc with chymopapain preparations.

SUMMARY OF BACKGROUND DATA

The occurrence of an allergic reaction during chemonucleolysis implies prior sensitization to components of the injected enzyme solution. The latex of the unripe fruit of the papaya plant Carica papaya, from which chymopapain is purified, contains another three immunologically distinct cysteine proteinases: 1) caricain (EC 3.4.22.30), 2) glycyl endopeptidase (EC 3.4.22.25), and 3) papain (EC 3.4.22.2).

METHODS

A dot-blot immunoassay was developed to quantify each enzyme in Chymodiactin. Total serum immunoglobulin E levels and specific immunoglobulin E antibody levels to each of the four papaya cysteine proteinases were assayed by an enzyme-linked immunoassay in 12 sera containing immunoglobulin E antibodies to Chymodiactin.

RESULTS

Chymodiactin contained 70% chymopapain, 20% caricain, 4% glycyl endopeptidase, and 0.1% papain. Immunoglobulin E antibodies to all four proteinases were found in most of the 12 sera, but in varying proportions. Antibodies to glycyl endopeptidase were predominant in eight sera, and the mean amounts of immunoglobulin E directed against each protein were: glycyl endopeptidase, 4.21 IU/ml; caricain, 2.9 IU/ml; chymopapain, 1.97 IU/ml; and papain, 1.39 IU/ml. Total serum immunoglobulin E levels showed little correlation with immunoglobulin E responses to Chymodiactin.

CONCLUSIONS

The results suggested that removal of glycyl endopeptidase and caricain from pharmaceutical preparations of chymopapain may help reduce the incidence of allergic reactions during chemonucleolysis.

The structural origins of the unusual specificities observed in the isolation of chymopapain M and actinidin by covalent chromatography and the lack of inhibition of chymopapain M by cystatin

1. The selectivity observed when the potentially general technique for the isolation of fully active forms of cysteine proteinases, covalent chromatography by thiol-disulphide interchange, is applied to chymopapain M and to actinidin was investigated by a combination of experimentation and computer modelling. Neither of these enzymes is able to react with the original Sepharose-GSH-2-dipyridyl disulphide gel, but fully active forms of both enzymes are obtained by using Sepharose-2-hydroxypropyl-2'-dipyridyl disulphide gel, which is both electrically neutral and sterically less demanding than the GSH gel. Electrostatic potential calculations, minimization and molecular-dynamics simulations provide explanations for the unusual, but different, specificities exhibited by actinidin and chymopapain M in the interactions of their active centres with ligands. 2. The unique behaviour of chymopapain M in exerting an almost absolute specificity for substrates with glycine at the P1 position and in resisting inhibition by cystatin was examined by the computer-modelling techniques. A new, modelled, structure of the complete chicken egg-white cystatin molecule based on the crystal structure of a short form of cystatin was deduced as a necessary prerequisite. The results suggest that electrostatic repulsion prevents reaction of actinidin with the GSH gel, whereas a steric 'cap' resulting from a unique arginine-65-glutamic acid-23 interaction in chymopapain M prevents reaction of the gel with this enzyme and accounts for the lack of its inhibition by cystatin and its specificity in catalysis. 3. Use of chymopapain M as a structural variant of papain demonstrates the validity of the predictions of Lowe and Yuthavong [Biochem. J. (1971) 124, 107-115] relating to the structural requirements and binding characteristics of the S1 subsite of papain.

Structure of chymopapain M the late-eluted chymopapain deduced by comparative modelling techniques and active-centre characteristics determined by pH-dependent kinetics of catalysis and reactions with time-dependent inhibitors: the Cys-25/His-159 ion-pair is insufficient for catalytic competence in both chymopapain M and papain

Chymopapain M, the monothiol cysteine proteinase component of the chymopapain band eluted after chymopapains A and B in cation-exchange chromatography, was isolated from the dried latex of Carica papaya and characterized by kinetic and chromatographic analysis. This late-eluted chymopapain is probably a component of the cysteine proteinase fraction of papaya latex discovered by Schack [(1967) Compt. Rend. Trav. Lab. Carlsberg 36, 67-83], named papaya peptidase B by Lynn [(1979) Biochim. Biophys. Acta 569, 193-201] and partially characterized by Polgár [(1981) Biochim. Biophys. Acta 658, 262-269] and is the enzyme with unusual specificity characteristics (papaya proteinase IV) that Buttle, Kembhavi, Sharp, Shute, Rich and Barrett [Biochem. J. (1989) 261, 469-476] claimed to be a previously undetected cysteine proteinase eluted from a cation-exchange column near to the early-eluted chymopapains. A study of the time-dependent chromatographic consequences of thiol-dependent proteolysis of the components of papaya latex is reported. Chymopapain M was isolated by (i) affinity chromatography followed by separation from papain using cation-exchange f.p.l.c. on a Mono S HR5/5 column and (ii) cation-exchange chromatography followed by an unusual variant of covalent chromatography by thiol-disulphide interchange. The existence in chymopapain M of a nucleophilic interactive Cys/His catalytic-site system analogous to those in papain (EC 3.4.22.2) and other cysteine proteinases was deduced from the characteristics shape of the pH-second-order rate constant (k) profiles for its reactions with 2,2'-dipyridyl disulphide and ethyl 2-pyridyl disulphide. Analysis of the pH-k data for the reactions of chymopapain M with the 2-pyridyl disulphides and with 4,4'-dipyridyl disulphide permits the assignment of molecular pKa values of 3.4 and 8.7 to the formation and subsequent dehydronation of the Cys-S-/His-Im+H state of the catalytic site and reveals three other kinetically influential ionizations with pKa values 3.4, 4.3 and 5.6. The pH-dependences of kcat./Km for the hydrolysis of N-acetyl-L-Phe-Gly-4-nitroanilide at 25.0 degrees C and I0.1 M catalysed by chymopapain M and papain were determined. For both enzymes, little catalytic activity (5-7% of the maximal) develops consequent on formation of the catalytic site Cys-S-/His-Im+H ion-pair state (across pKa 3.4 for both enzymes). For papain, full expression of Kcat./Km for the uncharged substrate requires only the additional hydronic dissociation with pKa 4.2. By contrast, full expression of kcat./Km for chymopapain M requires additional hydronic dissociation with pKa values of 4.3 and 5.6.(ABSTRACT TRUNCATED AT 400 WORDS)

Cooperativity in the unfolding transitions of cysteine proteinases. Calorimetric study of the heat denaturation of chymopapain and papain

Differential scanning calorimetry (DSC) was employed to study the thermal unfolding of chymopapain (EC 3.4.22.6) and papain (EC 3.4.22.2), two highly homologous cysteine proteinases from Carica papaya. Under all pH conditions used, both enzymes showed irreversible thermal denaturation. However, results from experiments performed at two different scanning rates suggest that interpretation of data in terms of equilibrium thermodynamics is not unreasonable. For papain, the ratio of calorimetric (delta Hcal) to van't Hoff (delta HvH) enthalpies approximated to 2.0. This value indicates that papain domains unfold almost independently, as it has been reported previously. In contrast, chymopapain displayed a more cooperative behavior with a delta Hcal to delta HvH ratio of 1.3-1.4. DSC curves were analyzed in terms of a mechanism that includes domain-domain interactions. The results showed a negligible interdomain free energy in the case of papain, but a significant value of approx. 1.0 kcal/mol (1 cal = 4.184 J) for chymopapain. These two proteins also differed in the unfolding heat-capacity change, delta Cp, which suggests that their native structures bury different amounts of nonpolar surface area.

Factors effecting the thermostability of cysteine proteinases from Carica papaya

Thermal denaturation of four Carica papaya cysteine proteinases (papain, chymopapain, papaya proteinases 3 and 4) was studied as a function of pH using high-sensitivity differential scanning calorimetry. The ratios of calorimetric enthalpy to Van't Hoff enthalpy suggest that, for all these proteins, denaturation occurs as a non two state process, via an intermediate structure. Differences in the thermal stabilities of the proteinases; chymopapain > papaya proteinase 3 > papain > papaya proteinase 4, were correlated to their amino acid sequence to explain the observations in terms of mobility and specific residue mutation. Three-dimensional structures of papain and papaya proteinase 3 were similarly used to illustrate the influence of atomic mobility on stability.