Catalysis of the refolding of urea denatured creatine kinase by peptidyl-prolyl cis-trans isomerase

Structure and evolution of the spliceosomal peptidyl-prolyl cis-trans isomerase Cwc27

Cwc27 is a spliceosomal cyclophilin-type peptidyl-prolyl cis-trans isomerase (PPIase). Here, the crystal structure of a relatively protease-resistant N-terminal fragment of human Cwc27 containing the PPIase domain was determined at 2.0 Å resolution. The fragment exhibits a C-terminal appendix and resides in a reduced state compared with the previous oxidized structure of a similar fragment. By combining multiple sequence alignments spanning the eukaryotic tree of life and secondary-structure prediction, Cwc27 proteins across the entire eukaryotic kingdom were identified. This analysis revealed the specific loss of a crucial active-site residue in higher eukaryotic Cwc27 proteins, suggesting that the protein evolved from a prolyl isomerase to a pure proline binder. Noting a fungus-specific insertion in the PPIase domain, the 1.3 Å resolution crystal structure of the PPIase domain of Cwc27 from Chaetomium thermophilum was also determined. Although structurally highly similar in the core domain, the C. thermophilum protein displayed a higher thermal stability than its human counterpart, presumably owing to the combined effect of several amino-acid exchanges that reduce the number of long side chains with strained conformations and create new intramolecular interactions, in particular increased hydrogen-bond networks.

Proteomics analysis of differential expression of cellular proteins in response to avian H9N2 virus infection in human cells

We present the first proteomic analysis on the cellular responses to avian influenza virus (H9N2) infection in a human cell line in different time courses in order to search for target proteins for viral pathogenesis/adaptation studies. By using 2-DE coupled with MALDI-TOF MS and nano-ESI-MS/MS, we identified a set of differentially expressed cellular proteins, including cytoplasmic actin, cytokeratin, prohibitin, enoyl-CoA hydratase, peptide-prolyl cis-trans isomerase A (PPIase A), chloride intracellular channel protein 1, pyruvate dehydrogenase E1 component subunit beta, adenine phosphoribosyltransferase, guanine nucleotide-binding protein subunit beta, nucleoside diphosphate kinase A, elongation factor 1-beta and splicing factor, arginine/serine rich 1. The most significant changes in different time courses were found in cytoplasmic actin and cytokeratin, both of which constituted the major components of cytoskeleton network in the cells. The obtained data suggested a possible role of the cytoskeleton during avian influenza virus infection of mammalian cells, which might help for better understanding of the dynamics of avian influenza virus and host interaction in mammalian cell setting.

Capture of monomeric refolding intermediate of human muscle creatine kinase

Human muscle creatine kinase (CK) is an enzyme that plays an important physiological role in the energy metabolism of humans. It also serves as a typical model for studying refolding of proteins. A study of the refolding and reactivation process of guanidine chloride-denatured human muscle CK is described in the present article. The results show that the refolding process can be divided into fast and slow folding phases and that an aggregation process competes with the proper refolding process at high enzyme concentration and high temperature. An intermediate in the early stage of refolding was captured by specific protein molecules: the molecular chaperonin GroEL and alpha(s)-casein. This intermediate was found to be a monomer, which resembles the "molten globule" state in the CK folding pathway. To our knowledge, this is the first monomeric intermediate captured during refolding of CK. We propose that aggregation is caused by interaction between such monomeric intermediates. Binding of GroEL with this intermediate prevents formation of aggregates by decreasing the concentration of free monomeric intermediates, whereas binding of alpha(s)-casein with this intermediate induces more aggregation.

Coexpression of folding accessory proteins for production of active cyclodextrin glycosyltransferase of Bacillus macerans in recombinant Escherichia coli

Coexpression of folding accessory proteins, molecular chaperones, and human peptidyl-prolyl cis-trans isomerase (PPIase) increased production of active cyclodextrin glycosyltransferase (CGTase) of Bacillus macerans, which is otherwise mainly expressed as inclusion body in recombinant Escherichia coli. The best partner for soluble expression of CGTase was found to be human PPIase followed by coexpression of DnaK-DnaJ-GrpE together with GroEL-GroES. Such a significant enhancement by human PPIase coexpression seemed to be due to dual functions of chaperone and peptidyl-prolyl cis-trans isomerization. Coexpression of GroEL-GroES or minichaperone alone did not influence the specific CGTase activity. For production of active CGTase in large amounts, a high cell density culture was achieved using a pH-stat fed-batch strategy. The optimized fed-batch fermentation resulted in dry cell weight of 103.4 g/L and CGTase activity of 1200 U/mL. Combination of human PPIase expression at a gene level and cell culture optimization at a process scale exerted a synergistic effect on the product yield of soluble CGTase expression in recombinant E. coli.

Unassisted refolding of urea-denatured arginine kinase from shrimp Feneropenaeus chinensis: evidence for two equilibrium intermediates in the refolding pathway

The refolding process and the equilibrium intermediates of urea-denatured arginine kinase (AK) were investigated by 1-anilino-8-naphthalenesulfonate (ANS) intrinsic fluorescence, far-UV circular dichroism (CD), size-exclusion chromatography (SEC), and enzymatic activity. In dilute denaturant, two equilibrium refolding intermediates (I and N') were discovered, and a refolding scheme of urea-denatured AK was proposed. During the refolding of urea-denatured AK, the fluorescence intensity increased remarkably, accompanied by a significant blue shift of the emission maximum and a pronounced increase in molar ellipticity of CD at 222 nm. The first folding intermediate (I) was inactive in urea solution ranging between 2.4 and 3.0 M. The second (N') existed between a 0.4- and 0.8-M urea solution, with slightly increased activity. Neither the blue shift emission maximum nor the molar ellipticity of CD at 222 nm showed significant changes in these two regions. The two intermediates were characterized by monitoring the ANS binding ability in various residual urea solutions, and two peaks of the emission intensity were observed in urea solutions of 0.6 and 2.8 M, respectively. The SEC results indicated that a distribution coefficient (K(D)) platform existed in urea solutions ranging between 2.4 and 3.0 M urea, suggesting that there was a similarly apparent protein profile and size in the urea solution region. The refolding kinetics showed that the urea-denatured AK was in two-phase refolding. Proline isomerization occurred in the unfolding process of AK, which blocked the slow phase of refolding. These results suggested that the refolding process of urea-denatured AK contained at the least two equilibrium refolding intermediates.

Effects of arginine on rabbit muscle creatine kinase and salt-induced molten globule-like state

The arginine (Arg)-induced unfolding and the salt-induced folding of creatine kinase (CK) have been studied by measuring enzyme activity, fluorescence emission spectra, native polyacrylamide gel electrophoresis and size exclusion chromatography (SEC). The results showed that Arg caused inactivation and unfolding of CK, but there was no aggregation during CK denaturation. The kinetics of CK unfolding followed a one-phase process. At higher concentrations of Arg (>160 mM), the CK dimers were fully dissociated, the alkali characteristic of Arg mainly led to the dissociation of dimers, but not denaturation effect of Arg's guanidine groups on CK. The inactivation of CK occurred before noticeable conformational changes of the whole molecules. KCl induced monomeric and dimeric molten globule-like states of CK denatured by Arg. These results suggest that as a protein denaturant, the effect of Arg on CK differed from that of guanidine and alkali, its denaturation for protein contains the double effects, which acts not only as guanidine hydrochloride but also as alkali. The active sites of CK have more flexibility than the whole enzyme conformation. Monomeric and dimeric molten globule-like states of CK were formed by the salt inducing in 160 and 500 mM Arg H(2)O solutions, respectively. The molten globule-like states indicate that monomeric and dimeric intermediates exist during CK folding. Furthermore, these results also proved the orderly folding model of CK.

Aggregation and folding of recombinant human creatine kinase

The processes of aggregation and refolding of recombinant human creatine kinase (rHCK) were studied. Most of the rHCK expressed in E. coli was present in the insoluble traction and it could be solubilized in 6 M urea solution. Unfolding of rHCK in 6 M urea showed biphasic kinetic courses (kappa1 = 6.5 x 10(-3) s(-1); kappa2 = 0.54 x 10(-3) s(-1)) as observed by maximum fluorescence wavelength change. During refolding of the rHCK dissolved in urea, significant aggregation was noticed following first-order kinetics. Aggregation rate constants were influenced by the concentration of NaCl, which increased the difference in transition-free energy (deltadeltaG), showing that stabilization of folding intermediates by NaCl could efficiently reduce the formation of insoluble aggregates. Formations of aggregate were also reduced by adjusting temperature, pH, and concentration of rHCK. Refolding of rHCK under the optimized condition which prevented the aggregation also showed multi-kinetic phases (kappa1 = 3.0 x 10(-3) s(-1); kappa2 = 0.64 x 10(-3) s(-1)). Under optimized conditions applied in this study, rHCK could correctly refold retrieving the high specific enzymatic activity.

Effects of aspartate on rabbit muscle creatine kinase and the salt induced molten globule state

The aspartate (Asp)-induced unfolding and the salt-induced folding of creatine kinase (CK) have been studied by measuring enzyme activity, fluorescence emission spectra, circular dichroism (CD) spectra, native polyacrylamide gel electrophoresis and ultraviolet difference spectra. The results showed that Asp caused inactivation and unfolding of CK, with no aggregation during CK denaturation. The kinetics of CK unfolding followed a one phase process. At higher concentrations of Asp (>2.5mM), the CK dimers were partially dissociated. Inactivation occurred before noticeable conformational change during CK denaturation. Asp denatured CK was mostly reactivated and refolded by dilution. KCl induced the molten globule state with compact structure after CK was denatured with 10mM Asp. These results suggest that the effect of Asp differed from that of other denaturants such as guanidine, HCl or urea during CK unfolding. Asp is a reversible protein denaturant and the molten globule state indicates that intermediates exist during CK folding.

Effect of osmolytes as folding aids on creatine kinase refolding pathway

The influence of osmolytes, including dimethysulfoxide, glycine, proline and sucrose, on the refolding and reactivation courses of guanidine-denatured creatine kinase was studied by fluorescence emission spectra, circular dichroism spectra, recovery of enzymatic activity and aggregation. The results showed that low concentrations of dimethysulfoxide (<20%), glycine (<0.5 M), proline (<1 M) and sucrose (<0.75 M) improved the refolding yields of creatine kinase, but high osmolyte concentrations decreased its recovery. Sucrose favored the secondary structural formation of creatine kinase. Proline and sucrose facilitated refolding of the protein to its original conformation, while dimethysulfoxide and proline accelerated the hydrophobic collapse of creatine kinase to a packed protein. During the aggregation of creatine kinase, dimethysulfoxide and sucrose inhibited aggregation of creatine kinase, as did proline, but glycine was unable to inhibit aggregation. These systematic observations further support the suggestion that osmolytes, including low concentrations of dimethysulfoxide, proline or sucrose, possibly play a chaperone role in the refolding of creatine kinase. The results also indicate that sucrose and free amino acids are not only energy substrates and organic components in vivo, but also help correct protein folding.

Chaperone-like activity of peptidyl-prolyl cis-trans isomerase during creatine kinase refolding

Porcine kidney 18 kD peptidyl-prolyl cis-trans isomerase (PPIase) belongs to the cyclophilin family that is inhibited by the immunosuppressive drug cyclosporin A. The chaperone activity of PPIase was studied using inactive, active, and alkylated PPIase during rabbit muscle creatine kinase (CK) refolding. The results showed that low concentration inactive or active PPIase was able to improve the refolding yields, while high concentration PPIase decreased the CK reactivation yields. Aggregation was inhibited by inactive or active PPIase, and completely suppressed at 32 or 80 times the CK concentration (2.7 microM). However, alkylated PPIase was not able to prevent CK aggregation. In addition, the ability of inactive PPIase to affect CK reactivation and prevent CK aggregation was weaker than that of active PPIase. These results indicate that PPIase interacted with the early folding intermediates of CK, thus preventing their aggregation in a concentration-dependent manner. PPIase exhibited chaperone-like activity during CK refolding. The results also suggest that the isomerase activity of PPIase was independent of the chaperone activity, and that the proper molar ratio was important for the chaperone activity of PPIase. The cysteine residues of PPIase may be a peptide binding site, and may be an essential group for the chaperone function.

Folding pathway for partially folded rabbit muscle creatine kinase

Rabbit muscle creatine kinase (CK) was modified by 5,5'-dithio-bis(2-nitrobenzoic acid) accompanied by 3 M guanidine hydrochloride denaturation to produce a partially folded state with modified thiol groups. The partially folded CK was in a monomeric state detected by size exclusion chromatography, native-polyacrylamide gel electrophoresis, circular dichroism, and intrinsic fluorescence studies. After dithiothreitol (DTT) treatment, about 70% CK activity was regained with a two-phase kinetic course. Rate constants calculated for regaining of activity and refolding were compared with those for CK modified with various treatments to show that refolding and recovery of activity were synchronized. To further characterize the partially folded CK state and its folding pathway, the molecular chaperone GroEL was used to evaluate whether it can bind with partly folded CK during refolding, and 1-anilinonaphthalene-8-sulfonate was used to detect the hydrophobic surface of the monomeric state of CK. The monomeric state of CK did not bind with GroEL, although it had a larger area of hydrophobic surface relative to the native state. These results may provide different evidence for the structural requirement of GroEL recognition to the substrate protein compared with previously reported results that GroEL bound with substrate proteins mainly through hydrophobic surface. The present study provides data for a monomeric intermediate trapped by the modification of the SH groups during the refolding of CK. Schemes are given for explaining both the partial folding CK pathway and the refolding pathway.Key words: creatine kinase; partially folded state; reactivation; refolding; GroEL; intermediate.

Role of proline, glycerol, and heparin as protein folding aids during refolding of rabbit muscle creatine kinase

Aggregation of 3 M guanidine hydrochloride denatured creatine kinase (ATP: creatine N-phosphotransferase, EC 2.7.3.2) occurs after dilution into the refolding solution. Proline, glycerol and heparin sodium act as folding aids which can effectively inhibit aggregation of creatine kinase during refolding. Proline at 1 M concentration, glycerol at 10% concentration and heparin at 25 mg/ml not only completely prevented creatine kinase aggregation but also enabled the creatine kinase to return to its native state as well as to recover most of its native activity. The reactivity after the aggregation was completely blocked by the presence of each folding aid reached 65-80% of the native activity. Results of turbidity, activity, intrinsic fluorescence and 1-anilinonaphthalene-8-sulfonate binding fluorescence measurements suggested that the effect of heparin differs from that of proline and glycerol in its artificial chaperone-like behavior. Heparin may bind with creatine kinase both in the native state and during the refolding course. The results showed that this heparin-creatine kinase complex favorably restored the creatine kinase reactivity.

Aggregation of creatine kinase during refolding and chaperonin-mediated folding of creatine kinase

The course of refolding and reactivation of urea-denatured creatine kinase (ATP; creatine N-phosphotransferase, EC 2.7.3.2) has been studied in the absence and presence of molecular chaperonin GroEL. The enzyme was denatured in Tris--HCl buffer containing 6 M urea for 1 h. In the refolding studies, the denatured enzyme was diluted 60-fold into the same buffer containing GroEL or not for activity, turbidity, fluorescence measurements and polyacrylamide gel electrophoresis. The results show that the reactivation process is dependent of creatine kinase concentration in the concentration range 2.5--4 microM. The levels of activity recovery decrease with increasing enzyme concentration because of the formation of wrong aggregates. The molecular chaperonin GroEL can bind the refolding intermediate of creatine kinase and thus prevent the formation of wrong aggregates. This intermediate is an inactive dimeric form that is in a conformation resembling the 'molten globule' state.

Reactivation kinetics of guanidine hydrochloride-denatured creatine kinase measured using the substrate reaction

Guanidine hydrochloride-denatured creatine kinase (CK) can very quickly form a dimer with reactivity when the denaturant is diluted into the reaction system in the presence of DTT or EDTA. Tsou's method and its applied equation [Tsou (1988), Adv. Enzymol. Rel. Areas Mol. Biol. 61, 381-436; Yang and Zhou (1998), Biochim. Biophys. Acta 1388, 190-198] were used to measure the kinetic reactivation rate constants and the reactivation degree for reassociated CK dimers. Partial reactivation (about 50% at best) occurred following a monophasic course during the substrate reaction when compared with previous time interval measurements. The reactivation degree increased with increasing DTT (0.1-5 mM) and EDTA (0.1-1 mM) concentrations. The apparent forward rate constants do not change with concentration, showing that the reactivation is a reversible first-order reaction, but not of complex formation type. However, the apparent forward rate constants do change with EDTA concentration, showing that the reactivation with EDTA is a reversible first-order reaction as well as of complex formation type. Excess DTT concentrations have an inhibitory effect, indicating that the excessive EDTA acts as a metal chealate not only for free Mg2+, but also for MgATP during the enzyme catalysis. This study shows that additional information about the reactivation of CK can be obtained from examining the substrate reaction. The possible refolding pathway of CK is discussed.

The two slow refolding processes of creatine kinase are catalyzed by cyclophilin

A burst phase occurs in the refolding kinetics of guanidine-denatured creatine kinase due to formation of an intermediate within the mixing dead time, with further refolding to the native state after the burst phase along a path following biphasic kinetics. In the presence of cyclophilin, the refolding rates of the two slow processes are accelerated and the values are proportional to the cyclophilin concentration. The activity of cyclophilin in accelerating the slow refolding processes of creatine kinase is totally inhibited by cyclosporin A, indicating that the cis-trans isomerization of the peptidyl-prolyl bonds is involved in the two slow refolding processes.

Two-state irreversible thermal denaturation of muscle creatine kinase

Thermal denaturation of creatine kinase from rabbit skeletal muscle has been studied by differential scanning calorimetry. The excess heat capacity vs. temperature profiles were independent of protein concentration, but strongly temperature scanning rate-dependent. It has been shown that thermal denaturation of creatine kinase satisfies the previously proposed validity criteria for the two-state irreversible model [Kurganov et al., Biophys. Chem.70 (1997) 125]. The energy activation value has been calculated to be 461.0 +/- 0.7 kJ/mol.

Reactivation and refolding of a partially folded creatine kinase modified by 5,5'-dithio-bis(2-nitrobenzoic acid)

Creatine kinase with its thiol groups modified by 5, 5'-dithio-bis(2-nitrobenzoic acid) has been shown to be partially folded in a monomeric state using fluorescence, circular dichroism, proteolysis, and size exclusion chromatography studies. In the presence of DTT, the partially folded modified creatine kinase can be reactivated and refolded following a biphasic course, suggesting the existence of a monomeric intermediate during the refolding of CK. The results provide evidence for our previously suggested model of the refolding pathway of urea-denatured creatine kinase.

Antibody catalysis of peptidyl-prolyl cis-trans isomerization in the folding of RNase T1

An antibody generated to an alpha-keto amide containing hapten 1 catalyzes the cis-trans isomerization of peptidyl-prolyl amide bonds in peptides and in the protein RNase T1. The antibody-catalyzed peptide isomerization reaction showed saturation kinetics for the cis-substrate, Suc-Ala-Ala-Pro-Phe-pNA, with a kcat/Km value of 883 s-1.M-1; the reaction was inhibited by the hapten analog 13 (Ki = 3. 0 +/- 0.4 microM). Refolding of denatured RNase T1 to its native conformation also was catalyzed by the antibody, with the antibody-catalyzed folding reaction inhibitable both by the hapten 1 and hapten analog 13. These results demonstrate that antibodies can catalyze conformational changes in protein structure, a transformation involved in many cellular processes.