How additives influence the refolding of immunoglobulin-folded proteins in a stepwise dialysis system. Spectroscopic evidence for highly efficient refolding of a single-chain Fv fragment

Human anti-gold antibodies: biofunctionalization of gold nanoparticles and surfaces with anti-gold antibodies

The interface molecules designed to exhibit molecular recognitions between different species have become attractive tools for the bottom-up fabrication and hybridization of nanostructured units. Here, we focus on antibodies with high binding ability and specificity to construct a novel biomolecule interface for recognizing an inorganic material. Careful selection from a phage-displayed library of variable region heavy and light Fv chains of human antibodies using enzyme-linked immunosorbent assay and surface plasmon resonance assay resulted in the identification of an antibody fragment, A14P-b2, with high affinity (KD = 1.7 nm) and specificity for gold materials. Our results indicated the potential usefulness of human antibody libraries and the effectiveness of the antibody framework for recognizing bulk material surfaces. Construction of bivalent and bispecific antibodies on the A14P-b2 platform with high affinity by means of fusion technology enabled the functionalization of gold nanoparticles and allowed selective protein accumulation on gold spots patterned on a silicon substrate. This type of antibody engineering is potentially applicable to bio-inspired materials and nanobiosensing.

Purification of truncated and mutated Chemotaxis Inhibitory Protein of Staphylococcus aureus--an anti-inflammatory protein

The Chemotaxis Inhibitory Protein of Staphylococcus aureus (CHIPS) binds and blocks the C5a receptor (C5aR) and formyl-peptide receptor (FPR). This way, CHIPS is a potent inhibitor of the immune cell recruitment associated with inflammation. Truncation of the protein and the introduction of mutations, shifts the expression towards the insoluble fraction of Escherichia coli, whereas the wild-type protein can be solubly expressed. A protocol for expression and tag independent purification of biologically active CHIPS variants has been established to enable further characterization of an improved CHIPS variant, called ADC-1004. The CHIPS variants were purified by washing of E. coli inclusion bodies followed by refolding and gel filtration. New techniques were utilized to optimize the purification process. Expression in inclusion bodies was increased by the use of Ultra Yield flasks and optimal refolding conditions were determined by the use of the iFOLD Refolding System 2. The folding and biological activity of the purified proteins were analyzed by circular dichroism (CD) spectroscopy and flow cytometry, respectively, and compared to solubly produced CHIPS(31-113) and wild-type CHIPS(1-121). We show that the CHIPS variants produced in inclusion bodies can be refolded and purified to achieve equal biological activity as solubly produced CHIPS(31-113) and wild-type CHIPS(1-121). The truncation causes minor structural changes while purification from inclusion bodies or the soluble fraction does not further affect the structure.

In-vitro phosphorylation activity by recombinant alpha and beta subunits of Bombyx mori casein kinase 2

To clarify the control mechanism of the catalytic activity of casein kinase 2 (CK2) during early embryonic development in the silkworm, Bombyx mori, we attempted an in-vitro functional analysis by using the recombinant alpha and beta subunits of B. mori CK2 (rBmCK2alpha and rBmCK2beta) produced in a bacterial system. The renatured rBmCK2alpha possessed protein kinase activity. When rBmCK2alpha and rBmCK2beta were reconstituted in an approximate 1:1 molar ratio, the catalytic activity was almost the same as that of rBmCK2alpha alone. The catalytic activity of rBmCK2alpha was inhibited by polylysine, which is one of the activators of CK2 activity. However, when using the reconstituted rBmCK2alpha and rBmCK2beta (rBmCK2), activation by polylysine was observed. We examined the influence of sorbitol and 3-hydroxykynurenine (3-OHK), which are contained mainly in diapause eggs, on the phosphorylation activity of rBmCK2. Three-OHK inhibited rBmCK2 activity, but sorbitol had no effect on it. Furthermore, a functional analysis using rBmCK2alpha and beta subunits of Drosophila melanogaster CK2 revealed that a difference in the C-terminal amino acid of the CK2beta subunit influenced the phosphorylation activity of rBmCK2alpha. These results may provide new insights for clarifying the control mechanism of B. mori casein kinase 2 in eggs.

Critical contribution of aromatic rings to specific recognition of polyether rings. The case of ciguatoxin CTX3C-ABC and its specific antibody 1C49

To address how proteins recognize polyether toxin compounds, we focused on the interaction between the ABC ring compound of ciguatoxin 3C and its specific antibody, 1C49. Surface plasmon resonance analyses indicated that Escherichia coli-expressed variable domain fragments (Fv) of 1C49 had the high affinity constants and slow dissociation constants typical of antigen-antibody interactions. Linear van't Hoff analyses suggested that the interaction is enthalpy-driven. We resolved the crystal structure of 1C49 Fv bound to ABC ring compound of ciguatoxin 3C at a resolution of 1.7A. The binding pocket of the antibody had many aromatic rings and bound the antigen by shape complementarity typical of hapten-antibody interactions. Three hydrogen bonds and many van der Waals interactions were present. We mutated several residues of the antibody to Ala, and we used surface plasmon resonance to analyze the interactions between the mutated antibodies and the antigen. This analysis identified Tyr-91 and Trp-96 in the light chain as hot spots for the interaction, and other residues made incremental contributions by conferring enthalpic advantages and reducing the dissociation rate constant. Systematic mutation of Tyr-91 indicated that CH-pi and pi-pi interactions between the aromatic ring at this site and the antigen made substantial contributions to the association, and van der Waals interactions inhibited dissociation, suggesting that aromaticity and bulkiness are critical for the specific recognition of polyether compounds by proteins.

Contributions of a disulfide bond to the structure, stability, and dimerization of human IgG1 antibody CH3 domain

Recombinant human monoclonal antibodies have become important protein-based therapeutics for the treatment of various diseases. The antibody structure is complex, consisting of beta-sheet rich domains stabilized by multiple disulfide bridges. The dimerization of the C(H)3 domain in the constant region of the heavy chain plays a pivotal role in the assembly of an antibody. This domain contains a single buried, highly conserved disulfide bond. This disulfide bond was not required for dimerization, since a recombinant human C(H)3 domain, even in the reduced state, existed as a dimer. Spectroscopic analyses showed that the secondary and tertiary structures of reduced and oxidized C(H)3 dimer were similar, but differences were observed. The reduced C(H)3 dimer was less stable than the oxidized form to denaturation by guanidinium chloride (GdmCl), pH, or heat. Equilibrium sedimentation revealed that the reduced dimer dissociated at lower GdmCl concentration than the oxidized form. This implies that the disulfide bond shifts the monomer-dimer equilibrium. Interestingly, the dimer-monomer dissociation transition occurred at lower GdmCl concentration than the unfolding transition. Thus, disulfide bond formation in the human C(H)3 domain is important for stability and dimerization. Here we show the importance of the role played by the disulfide bond and how it affects the stability and monomer-dimer equilibrium of the human C(H)3 domain. Hence, these results may have implications for the stability of the intact antibody.

Correlation Between Thermal Aggregation and Stability of Lysozyme with Salts Described by Molar Surface Tension Increment: An Exceptional Propensity of Ammonium Salts as Aggregation Suppressor

Protein aggregation is a critical problem for biotechnology and pharmaceutical industries. Despite the fact that soluble proteins have been used for many applications, our understanding of the effect of the solution chemistry on protein aggregation still remains to be elucidated. This paper investigates the process of thermal aggregation of lysozyme in the presence of various types of salts. The simple law was found; the aggregation rate of lysozyme increased with increasing melting temperature of the protein (T (m)) governed by chemical characteristics of additional salts. Ammonium salts were, however, ruled out; the aggregation rates of lysozyme in the presence of the ammonium salts were smaller than the ones estimated from T (m). Comparing with sodium salts, ammonium salts increased the solubility of the hydrophobic amino acids, indicating that ammonium salts adsorb the hydrophobic region of proteins, which leads to the decrease in aggregation more effectively than sodium salts. The positive relation between aggregation rate and T (m) was described by another factor such as the surface tension of salt solutions. Fourier transform infrared spectral analysis showed that the thermal aggregates were likely to form beta-sheet in solutions that give high molar surface tension increment. These results suggest that protein aggregation is attributed to the surface free energy of the solution.

Expression and detection strategies for an scFv fragment retaining the same high affinity than Fab and whole antibody: Implications for therapeutic use in prion diseases

Since antibodies currently constitute the most rapidly growing class of human therapeutics, the high-yield production of recombinant antibodies and antibody fragments is a real challenge. Using as model a monoclonal antibody directed against the human prion protein that we prepared previously and tested for its therapeutic value, we describe here experimental conditions allowing the production of large quantities (up to 35 mg/l of bacterial culture) of correctly refolded and totally functional single chain fragment variable (scFv). These quantities were sufficient to characterize the binding properties of this small recombinant fragment through in vitro and ex vivo approaches. Interestingly, this scFv retains full binding capacity for its antigen, i.e. the human prion protein, when compared with the corresponding Fab or whole antibody, and recognizes soluble, solid-phase-adsorbed, and membrane-bound prion protein. This strongly suggests that from the mAb cloning step to the refolding of the recombinant fragment, each stage is well controlled, leading to almost 100% functional scFv. These results are of interest not only in view of possible immunotherapy for prion diseases, but also more generally in emphasizing the great promise of these small recombinant molecules in the context of targeted therapies.

Expression and purification of two anti-CD19 single chain Fv fragments for targeting of liposomes to CD19-expressing cells

Antibody-targeted liposomal anticancer drugs combine the specificity of antibodies with large payloads of entrapped drugs. We previously showed that liposomal doxorubicin (DXR) targeted via anti-CD19 monoclonal antibodies (mAb) or their Fab' fragments against the B-cell antigen CD19 led to improved therapeutic effects in murine B-cell lymphoma models relative to non-targeted liposomal DXR. We now are examining the use of anti-CD19 single chain fragments of the antibody variable region (scFv) as a targeting moiety, to test the hypothesis that scFv have advantages over full-sized mAb or Fab' fragments. We expressed two different anti-CD19 scFv constructs, HD37-C and HD37-CCH in E. coli, and purified the scFvs using two different methods. The HD37-CCH construct was selected for coupling studies due to its relative stability and activity in comparison to HD37-C. When coupled to liposomes, the HD37-CCH scFv showed increased binding in vitro to CD19-positive Raji cells, compared to non-targeted liposomes. Cytotoxicity data showed that HD37-CCH scFv-targeted liposomes loaded with DXR were more cytotoxic than non-targeted liposomal DXR. Our results suggest that anti-CD19 scFv constructs should be explored further for their potential in treating B-lymphoid leukemias and lymphomas.

Suppression of protein interactions by arginine: a proposed mechanism of the arginine effects

Arginine has been used to suppress protein aggregation and protein-protein or protein-surface interactions during protein refolding and purification. While its biotechnology applications are gradually expanding, the mechanism of these effects of arginine has not been fully elucidated. Arginine is more effective at higher concentrations, an indication of weak interactions with the proteins. The effects of weakly interacting additives, such as arginine, on protein solubility, stability and aggregation have been explained from three different approaches: i.e., (1) the effects of additives on the structure of water, (2) the interactions of additives with the amino acid side chains and peptide bonds and (3) the preferential interactions of additives with the proteins. Here we have examined these properties of arginine and compared with those of other additives, e.g., guanidine hydrochloride (GdnHCl) and certain amino acids and amines. GdnHCl is a strong salting-in agent and denatures proteins, while betaine is a protein stabilizer. Several amino acids and amine compounds, including betaine, which stabilize the proteins, are strongly excluded; i.e., the proteins are preferentially hydrated in these solutions. On the other hand, GdnHCl preferentially binds to the proteins. Arginine is intermediate between these two extreme cases and shows a more complicated pattern of interactions with the proteins. The effects of additives on water structure, e.g., the surface tension of aqueous solution of the additives and the solubility of amino acids in the presence of additives also shed light on the mechanism of the effects of the additives on protein aggregation. While arginine increases the surface tension of water, it favorably interacts with most amino acid side chains and the peptide bonds, a property shared with GdnHCl. Thus, we propose that while arginine is similar to GdnHCl in the amino acid level, arginine interacts with the proteins differently from GdnHCl.

Activation of a Refolded, Berberine-specific, Single-chain Fv Fragment by Addition of Free Berberine

A single-chain variable fragment (scFv) specific for berberine was produced in Escherichia coli. The anti-berberine scFv gene was cloned from hybridoma 1D5-3B-7 producing the monoclonal antibody. The variable regions of the heavy (V(H)) and light chain (V(L)) genes were connected with a flexible linker using an assembly PCR. The V(H)-linker-V(L) gene was inserted into a plasmid, pET28a (+), then overexpressed in E. coli BL21 (DE3). The active of the scFv by refolding based on stepwise dialysis methods and an artificial chaperone was determined by direct and competitive enzyme-linked immunosorbent assay (ELISA). The results of direct ELISA showed that the anti-berberine scFv retained specific binding activity to berberine. In competitive ELISA, however, activity was increased depending on the concentration of berberine.

Arginine inhibits Na-driven flagellar motors of alkaliphilic Bacillus

L-arginine has attracted a great deal of attention as an agent for refolding denatured proteins, and the mildness of its effects offer hope for a wide range of potential applications for this substance, including medicines with few side effects. We report that both L- and D-arginine inhibits Na+-driven flagellar motors of alkaliphilic Bacillus by competing with Na+, which we take as evidence that arginine specifically binds to a molecular target.

Solubilization and refolding of bacterial inclusion body proteins

Inclusion bodies produced in Escherichia coli are composed of densely packed denatured protein molecules in the form of particles. Refolding of inclusion body proteins into bioactive forms is cumbersome, results in poor recovery and accounts for the major cost in production of recombinant proteins from E. coli. With new information available on the structure and function of protein aggregates in bacterial inclusion bodies, it has been possible to develop improved solubilization and refolding procedures for higher recovery of bioactive protein. Inclusion bodies are formed from partially folded protein intermediates and are composed of aggregates of mostly single types of polypeptide. This helps to isolate and purify the protein aggregates to homogeneity before solubilization and refolding. Proteins inside inclusion body aggregates have native-like secondary structures. It is assumed that restoration of this native-like secondary structure using mild solubilization conditions will help in improved recovery of bioactive protein in comparison to solubilization using a high concentration of chaotropic agent. Analysis of the dominant forces causing aggregation during inclusion body formation provides information to develop suitable mild solubilization procedures for inclusion body proteins. Refolding from such solubilized protein will be very high due to restoration of native-like secondary structure. Human growth hormone inclusion bodies were purified to homogeneity from E. coli cells before solubilization and refolding. Pure inclusion bodies were solubilized at alkaline pH in the presence of 2 M urea solution. The solubilized proteins were refolded using a pulsatile renaturation process and subsequently purified using chromatographic procedures. More than 40% of the inclusion body proteins could be refolded back to the bioactive native conformation. Mild solubilization is thus the key for high recovery of bioactive protein from inclusion bodies.

Arginine as an effective additive in gel permeation chromatography

A major problem in gel permeation chromatography (GPC) or size exclusion chromatography is non-specific binding of applied proteins to the column matrix (stationary phase). We have tested an aqueous arginine solution as the GPC mobile phase on silica-based and polymer-based columns, using mouse monoclonal antibody and recombinant human activin, interleukin-6, basic fibroblast growth factor, and interferon-gamma as model proteins. We observed that addition of arginine to the mobile phase improves separation of the proteins and their soluble aggregates from the GPC columns, which suggests that arginine is an effective additive for the GPC mobile phase.

Is arginine a protein-denaturant?

Arginine is a useful solvent additive for many applications, including refolding and solubilization of proteins from insoluble pellets, and suppression of protein aggregation and non-specific adsorption during formulation and purification. However, there is a concern that arginine may be a protein-denaturant, which may limit the expansion of its applications. Such concern arises from the facts that arginine decreases melting temperature and perturbs the spectroscopic properties of certain proteins and contains a guanidinium group, which is a critical chemical structure for denaturing activity of guanidine hydrochloride. Here, we show that although arginine does lower the melting temperatures of certain proteins, the extent is insufficient to cause denaturation of proteins at or below room temperature. The proteins described here show enzymatic activity and folded structure in the presence of arginine, although the local structure around aromatic amino acids is perturbed by arginine. Arginine differs from guandinine hydrochloride in the mode of interactions with proteins, which may be a primary reason why arginine is not a protein-denaturant.

Mouse Polycomb M33 is required for splenic vascular and adrenal gland formation through regulating Ad4BP/SF1 expression

Mice with disrupted mammalian PcG (Polycomb group) genes commonly show skeletal transformation of anterior-posterior identities. Disruption of the murine M33 gene, a PcG member, displayed posterior transformation of the vertebral columns and sternal ribs. In addition, failure of T-cell expansion and hypoplasia and sex-reversal of the gonads, have been observed. In the present study, we identified defects in the splenic and adrenal formation of M33-knock-out (KO) mice on a C57BL/6 genetic background. The spleen in these animals was smaller than in the wild-type mice and was spotted red because of nonuniform distribution of blood cells. Histologic examination revealed disorganization of the vascular endothelium and its surrounding structures, and immunohistochemistry demonstrated disturbances in vascular formation and colonization of immature hematopoietic cells. These splenic phenotypes observed in the M33-KO mice were quite similar to those seen in Ad4BP/SF1 (Nr5a1) knock-outs. Moreover, the adrenal glands of M33-KO and Ad4BP/SF1 heterozygous KO mice were smaller than those of the wild-type mice. Western blot, immunohistochemistry, and reverse transcriptase-polymerase chain reaction (RT-PCR) analyses of the M33 knock-outs all indicated significantly low expression of adrenal 4 binding protein/steroidogenic factor-1 (Ad4BP/SF-1), indicating that M33 is an essential upstream regulator of Ad4BP/SF1. In agreement with these observations, chromatin immunoprecipitation assays with adrenocortical Y-1 cells revealed direct binding of the M33-containing PcG to the Ad4BP/SF1 gene locus.

High-throughput automated refolding screening of inclusion bodies

One of the main stumbling blocks encountered when attempting to express foreign proteins in Escherichia coli is the occurrence of amorphous aggregates of misfolded proteins, called inclusion bodies (IB). Developing efficient protein native structure recovery procedures based on IB refolding is therefore an important challenge. Unfortunately, there is no "universal" refolding buffer: Experience shows that refolding buffer composition varies from one protein to another. In addition, the methods developed so far for finding a suitable refolding buffer suffer from a number of weaknesses. These include the small number of refolding formulations, which often leads to negative results, solubility assays incompatible with high-throughput, and experiment formatting not suitable for automation. To overcome these problems, it was proposed in the present study to address some of these limitations. This resulted in the first completely automated IB refolding screening procedure to be developed using a 96-well format. The 96 refolding buffers were obtained using a fractional factorial approach. The screening procedure is potentially applicable to any nonmembrane protein, and was validated with 24 proteins in the framework of two Structural Genomics projects. The tests used for this purpose included the use of quality control methods such as circular dichroism, dynamic light scattering, and crystallogenesis. Out of the 24 proteins, 17 remained soluble in at least one of the 96 refolding buffers, 15 passed large-scale purification tests, and five gave crystals.

Identification, evolution, and regulation of expression of Guinea pig trappin with an unusually long transglutaminase substrate domain

Trappins are found in human, bovine, hippopotamus, and members of the pig family, but not in rat and mouse. To clarify the evolution of the trappin genes and the functional significance of their products, we isolated the trappin gene in guinea pig, a species belonging to a rodent family distinct from rat and mouse. Guinea pig trappin was confirmed to encode the same domain structure as trappin, consisting of a signal sequence, an extra large transglutaminase substrate domain, and a whey acidic protein motif. Northern blot analysis and in situ hybridization histochemistry as well as immunohistochemistry demonstrated that guinea pig trappin is expressed solely in the secretory epithelium of the seminal vesicle and that its expression is androgen-dependent. We confirmed that guinea pig trappin is cross-linked by prostate transglutaminase and that the whey acidic protein motif derived from guinea pig trappin has an inhibitory activity against leukocyte elastase. Genome sequence analysis showed that guinea pig trappin belongs to the family of REST (rapidly evolving seminal vesicle transcribed) genes.

Nondenaturing solubilization of β2 microglobulin from inclusion bodies by l-arginine

Expression of beta2 microglobulin (beta2m) in Escherichia coli resulted in formation of inclusion bodies. Attenuated total reflectance Fourier transform infrared analysis suggested a native-like secondary structure of beta2m in the inclusion bodies. Nondenaturing solubilization of the native-like beta2m from inclusion bodies was achieved using L-arginine solution, which enables an efficient recovery of beta2m with little aggregation. Greater beta2m solubilization from inclusion bodies was obtained at higher temperatures. Low-temperature solubilization yielded beta2m with fluorescence properties identical to those of native beta2m, but its secondary structure was slightly nonnative. Solubilization at moderate temperature gave beta2m with an apparently native structure. We propose an efficient nondenaturing solubilization method combining L-arginine and moderate temperature.

Solubility of disulfide-bonded proteins in the cytoplasm of Escherichia coli and its “oxidizing” mutant

AIM: To study the influence of redox environment of Escherichia coli (E. coli) cytoplasm on disulfide bond formation of recombinant proteins.

METHODS: Bovine fibroblast growth factor (BbFGF) was selected as a model of simple proteins with a single disulfide bond and free cysteines. Anti-HBsAg single-chain Fv (HBscFv), an artificial multidomain protein, was selected as the model molecule of complex protein with 2 disulfide bonds. A BbFGF-producing plasmid, pJN-BbFGF, and a HBscFv producing-plasmid, pQE-HBscFv, were constructed and transformed into E. coli strains BL21(DE3) and M15[pREP4] respectively. At the same time, both plasmids were transformed into a reductase-deficient host strain, E. coli Origami(DE3). The 4 recombinant E. coli strains were cultured and the target proteins were purified. Solubility and bioactivity of recombinant BbFGF and HBscFv produced in different host strains were analyzed and compared respectively.

RESULTS: All recombinant E. coli strains could efficiently produce target proteins. The level of BbFGF in BL21(DE3) was 15-23% of the total protein, and was 5-10% in Origami (DE3). In addition, 65% of the BbFGF produced in BL21(DE3) formed into inclusion body in the cytoplasm, and all the target proteins became soluble in Origami(DE3). The bioactivity of BbFGF purified from Origami(DE3) was higher than its counterpart from BL21(DE3). The ED₅₀ of BbFGF from Origami(DE3) and BL21(DE3) was 1.6 μg/L and 2.2 μg/L, respectively. Both HBscFv formed into inclusion body in the cytoplasm of M15[pQE-HBscFv] or Origami[pQE-HBscFv]. But the supernatant of Origami[pQE-HBscFv] lysate displayed weak bioactivity and its counterpart from M15[pQE-HBscFv] did not display any bioactivity. The soluble HBscFv in Origami[pQE-HBscFv] was purified to be 1-2 mg/L and its affinity constant was determined to be 2.62×10⁷ mol/L. The yield of native HBscFv refolded from inclusion body in M15[pQE-HBscFv] was 30-35 mg/L and the affinity constant was 1.98×10⁷ mol/L. There was no significant difference between the bioactivity of HBscFvs refolded from the inclusion bodies produced in different host strains.

CONCLUSION: Modification of the redox environment of E. coli cytoplasm can significantly improve the folding of recombinant disulfide-bonded proteins produced in it.

Prevention of genital herpes in a guinea pig model using a glycoprotein D-specific single chain antibody as a microbicide

Background

Genital herpes (GH) is a recurrent sexually transmitted infection (STI) that causes significant morbidity and is also the major source of herpes simplex virus (HSV) in cases of neonatal herpes. Vaccination is a current goal which has had limited success so far in preventing GH and microbicides offer an attractive alternative. Treatment of primary disease cannot prevent establishment of latent infections and thus, cannot prevent subsequent recurrent disease. Recently, many of the molecular events leading to entry of HSV into cells have been elucidated, resulting in the description of a number of herpesvirus entry mediators (HVEMs) that interact with HSV glycoprotein D (gD) on the surface of virions. Described here is a strategy for interrupting the spread of HSV based on interfering with these interactions. The hypothesis addressed in the current report was that single chain antibody variable fragments (scFv) that interrupt associations between gD and HVEMs would not only prevent infection in vitro but could also be used as microbicides to interfere with acquisition GH.

Results and Conclusions

Here we show that a scFv derived from a particular hybridoma, DL11, not only inhibits infection in vitro but also prevents development of GH in a guinea pig model when applied intravaginally in an inert vehicle. Comparison of different anti-gD single chain antibodies supported the hypothesis that the activity of DL11-scFv is based on its ability to disrupt the associations between gD and the two major receptors for HSV, nectin-1 and HveA. Further, the results predict that bacterial expression of active single chain antibodies can be optimized to manufacture inexpensively a useful microbicidal product active against HSV.

Androgen-Dependent Expression, Gene Structure, and Molecular Evolution of Guinea Pig Caltrin II, a WAP-Motif Protein1

We determined the cDNA and gene structures of guinea pig caltrin II, a unique member of the calcium transporter inhibitors containing a whey acidic protein (WAP) motif, and we established that it is a secretory protein with a potential 21-amino acid signal peptide in its N-terminus. Northern blot analysis and in situ hybridization histochemistry indicated that the expression of caltrin II is restricted to luminal epithelial cells in the seminal vesicles. Its message levels markedly decreased either after castration (and were restored by simultaneous administration of testosterone) or after treatment of the animals with estradiol, suggesting that the expression of caltrin II is androgen-dependent. Recombinant caltrin II had an elastase-inhibitor activity. Comparison of sequence between the caltrin II and related genes and their molecular evolutionary analyses revealed that caltrin II and seminal vesicle secretory proteins (SVPs) appear to be evolved from a common ancestor gene that is made by the fusion of semenogelin and trappin genes. Caltrin II and SVPs lost the transglutaminase substrate domain and the WAP motif, respectively, within a single exon, resulting in the exertion of different functions.

Structural characteristics and refolding of in vivo aggregated hyperthermophilic archaeon proteins

Several recombinant proteins in inclusion bodies expressed in Escherichia coli have been measured by Fourier transform infrared and solid-state nuclear magnetic resonance spectra to provide the secondary structural characteristics of the proteins from hyperthermophilic archaeon Pyrococcus horikoshii OT3 (hyperthermophilic proteins) in inclusion bodies. The beta-strand-rich single chain Fv fragment (scFv) and alpha-helix-rich interleukin (IL)-4 lost part of the native-like secondary structure in inclusion bodies, while the inclusion bodies composed of the hyperthermophilic proteins of which the native form is alpha-helix rich, are predominated by alpha-helix structure. Further, the secondary structure of the recombinant proteins solubilized from inclusion bodies by detergent or denaturant was observed by circular dichroism (CD) spectra. The solubilization induced the denaturation of the secondary structure for scFv and IL-4, whereas the solubilized hyperthermophilic proteins have retained the alpha-helix structure with the CD properties resembling those of their native forms. This indicates that the hyperthermophilic proteins form native-like secondary structure in inclusion bodies. Refolding of several hyperthermophilic proteins from in vivo aggregated form without complete denaturation could be accomplished by solubilization with lower concentration (e.g. 2 M) of guanidine hydrochloride and removal of the denaturant via stepwise dialysis. This supports the existence of proteins with native-like structure in inclusion bodies and suggests that non-native association between the secondary structure elements leads to in vivo aggregation. We propose a refolding procedure on the basis of the structural properties of the aggregated archaeon proteins.

Solubilization of active green fluorescent protein from insoluble particles by guanidine and arginine

Expression of green fluorescent protein (GFP) in Escherichia coli (E. coli) resulted in only small amount of soluble and fluorescent GFP protein and hence most of the protein in insoluble particles. The expressed GFP in insoluble particles, however, was fluorescent, indicating that it is at least in part folded with an intact chromophore. The GFP in insoluble particles could not be solubilized by an aqueous (denaturant-free) buffer. Solubilization of active GFP from insoluble particles was then attempted with guanidine hydrochloride (GdnHCl), a strong protein-denaturant, or L-arginine, an aggregation suppressor. Solubilization from insoluble particles by 6M GdnHCl led to complete denaturation of the GFP existing in insoluble particles, while GdnHCl solution at lower concentration could solubilize fluorescent GFP. Solubilization of fluorescently active GFP from insoluble particles was also achieved by L-arginine. It is noteworthy that L-arginine was stronger in solubilizing insoluble GFP than GdnHCl below 2M. These results demonstrate that some proteins expressed in E. coli may form insoluble particles containing native conformation and L-arginine may be used to recover the proteins in the native form from such insoluble particles.

Prevention of thermal inactivation and aggregation of lysozyme by polyamines

Proteins tend to form inactive aggregates at high temperatures. We show that polyamines, which have a relatively simple structure as oligoamids, effectively prevent thermal inactivation and aggregation of hen egg lysozyme. In the presence of additives, including arginine and guanidine (100 microM), more than 30% of 0.2 mg x mL(-1) lysozyme in sodium phosphate buffer (pH 6.5) formed insoluble aggregates by heat treatment (98 degrees C for 30 min). However, in the presence of 50 mm spermine or spermidine, no aggregates were observed after the same heat treatment. The residual activity of lysozyme after this heat treatment was very low (< 5%), even in the presence of 100 microM arginine and guanidine, while it was maintained at approximately 50% in the presence of 100 microM spermine and spermidine. These results imply that polyamines are new candidates as molecular additives for preventing the thermal aggregation and inactivation of heat-labile proteins.

The effects of arginine on refolding of aggregated proteins: not facilitate refolding, but suppress aggregation

Arginine is one of the universal reagents that are effective in assisting refolding of recombinant proteins from inclusion bodies. The mechanism of the effects of arginine on refolding has remained, however, to be elucidated. Here we show that arginine does not stabilize proteins against heat treatment, as demonstrated by little change in melting temperature. It does increase reversibility of thermal melting and reduce aggregation under thermal stress. The observations suggest that arginine may not facilitate refolding, but may suppress aggregation of the proteins during refolding.