Refolding, structural transition and spermatozoa-binding of recombinant bonnet monkey (Macaca radiata) zona pellucida glycoprotein-C expressed in Escherichia coli

Expression, Solubilization, Refolding and Final Purification of Recombinant Proteins as Expressed in the form of "Classical Inclusion Bodies" in E. coli

Escherichia coli has been most widely used for production of the recombinant proteins. Over-expression of the recombinant proteins is the mainspring of the inclusion bodies formation. The refolding of these proteins into bioactive forms is cumbersome and partly time-consuming. In the present study, we reviewed and discussed most issues regarding the recovery of "classical inclusion bodies" by focusing on our previous experiences. Performing proper methods of expression, solubilization, refolding and final purification of these proteins, would make it possible to recover higher amounts of proteins into the native form with appropriate conformation. Generally, providing mild conditions and proper refolding buffers, would lead to recover more than 40% of inclusion bodies into bioactive and native conformation.

Kinetics of inclusion body formation and its correlation with the characteristics of protein aggregates in Escherichia coli

The objective of the research was to understand the structural determinants governing protein aggregation into inclusion bodies during expression of recombinant proteins in Escherichia coli. Recombinant human growth hormone (hGH) and asparaginase were expressed as inclusion bodies in E.coli and the kinetics of aggregate formation was analyzed in details. Asparaginase inclusion bodies were of smaller size (200 nm) and the size of the aggregates did not increase with induction time. In contrast, the seeding and growth behavior of hGH inclusion bodies were found to be sequential, kinetically stable and the aggregate size increased from 200 to 800 nm with induction time. Human growth hormone inclusion bodies showed higher resistance to denaturants and proteinase K degradation in comparison to those of asparaginase inclusion bodies. Asparaginase inclusion bodies were completely solubilized at 2–3 M urea concentration and could be refolded into active protein, whereas 7 M urea was required for complete solubilization of hGH inclusion bodies. Both hGH and asparaginase inclusion bodies showed binding with amyloid specific dyes. In spite of its low β-sheet content, binding with dyes was more prominent in case of hGH inclusion bodies than that of asparaginase. Arrangements of protein molecules present in the surface as well as in the core of inclusion bodies were similar. Hydrophobic interactions between partially folded amphiphillic and hydrophobic alpha-helices were found to be one of the main determinants of hGH inclusion body formation. Aggregation behavior of the protein molecules decides the nature and properties of inclusion bodies.

Solubilization of inclusion body proteins using n-propanol and its refolding into bioactive form

Inclusion bodies of recombinant human growth hormone (r-hGH) were isolated from Escherichia coli, enriched and solubilized in 100mM Tris buffer containing 6M n-propanol and 2M urea. Around 4 mg/ml of r-hGH from inclusion bodies were solubilized in 6M n-propanol-based buffer containing 2M urea. Existence of native-like secondary structure of r-hGH in 6M n-propanol solution was confirmed by CD and fluorescence spectra. Solubilized r-hGH was subsequently refolded by pulsatile dilution, purified to homogeneity and found to be functionally active. Tris buffer containing 6M n-propanol and 2M urea also effectively solubilized a number of proteins expressed as inclusion bodies in E. coli. Mild solubilization of inclusion body proteins, chaotropic effect of n-propanol at high concentration and kosmotropic effect at lower concentration helped in improved refolding of the solubilized protein. Around 40% of the r-hGH in the form of inclusion body aggregates was refolded into bioactive form while using n-propanol as solubilization agent. Solubilization with 6M n-propanol solution thus can be a viable alternative for achieving high throughput recovery of bioactive protein from inclusion bodies of E. coli.

Access to gram scale amounts of functional globular adiponectin from E. coli inclusion bodies by alkaline-shock solubilization

The adipose tissue derived protein adiponectin exerts anti-diabetic, anti-inflammatory and anti-atherosclerotic effects. Adiponectin serum concentrations are in the microgram per milliliter range in healthy humans and inversely correlate with obesity and metabolic disorders. Accordingly, raising circulating adiponectin levels by direct administration may be an intriguing strategy in the treatment of obesity-related metabolic disorders. However production of large amounts of recombinant adiponectin protein is a primary obstacle so far. Here, we report a novel method for large amount production of globular adiponectin from E. coli inclusion bodies utilizing an alkaline-shock solubilization method without chaotropic agents followed by precipitation of the readily renaturing protein. Precipitation of the mildly solubilized protein capitalizes on advantages of inclusion body formation. This approach of inclusion body protein recovery provides access to gram scale amounts of globular adiponectin with standard laboratory equipment avoiding vast dilution or dialysis steps to neutralize the pH and renature the protein, thus saving chemicals and time. The precipitated protein is readily renaturing in buffer, is of adequate purity without a chromatography step and shows biological activity in cultured MCF7 cells and significantly lowered blood glucose levels in mice with streptozotocin induced type 1 diabetes.

High throughput purification of recombinant human growth hormone using radial flow chromatography

Recombinant human growth hormone (r-hGH) was expressed in Escherichia coli as inclusion bodies. Using fed-batch fermentation process, around 670 mg/L of r-hGH was produced at a cell OD600 of 35. Cell lysis followed by detergent washing resulted in semi-purified inclusion bodies with more than 80% purity. Purified inclusion bodies were homogenous in preparation having an average size of 0.6 microm. Inclusion bodies were solubilized at pH 12 in presence of 2M urea and refolded by pulsatile dilution. Refolded protein was purified with DEAE-anion exchange chromatography using both radial and axial flow column (50 ml bed volume each). Higher buffer flow rate (30 ml/min) in radial flow column helped in reducing the batch processing time for purification of refolded r-hGH. Radial column based purification resulted in high throughput recovery of diluted refolded r-hGH in comparison to axial column. More than 40% of inclusion body protein could be refolded into bioactive form using the above method in a single batch. Purified r-hGH was analyzed by mass spectroscopy and found to be bioactive by Nb2 cell line proliferation assay. Inclusion body enrichment, mild solubilization, pulsatile refolding and radial flow chromatography worked co-operatively to improve the overall recovery of bioactive protein from inclusion bodies.

Molecular cloning and characterization of three distinct choriogenins in masu salmon, Oncorhynchus masou

Three cDNAs, each encoding a different choriogenin (Chg), were isolated from a female masu salmon (Oncorhynchus masou) liver cDNA library. Two of the cDNA clones, Chg Halpha and Chg Hbeta, showed a close relationship and contained the typical domains of zona pellucida (ZP) B genes in fish, namely proline and glutamine rich repeats, a trefoil factor family domain, and a ZP domain. Specific antibodies against recombinant Chg H products (rmHalpha and rmHbeta) were generated to elucidate the relationship between the Chg H cDNAs and two types of serum Chg H protein, which were previously purified and characterized, and designated as very-high-molecular-weight vitelline envelope-related protein (vhVERP) and Chg H of masu salmon. The immunobiochemical analyses revealed that the Chg Halpha and Chg Hbeta clones encoded vhVERP and Chg H proteins, respectively. The third cDNA clone (Chg L) appeared to be a ZPC gene and, by mapping the N-terminal sequence of purified Chg L, was shown to encode serum Chg L protein. Various types of heteromultimer of the three Chgs were identified immunologically as high molecular weight chorion components, indicating the involvement of complex heterodimerization of multiple Chgs in the construction of chorion architecture in masu salmon.

Polypeptide backbone derived from carboxyl terminal of mouse ZP3 inhibits sperm-zona binding

For mammalian organism, fertilization begins with species-specific recognition between sperm and egg, a process depending upon egg zona pellucida glycoproteins and putative sperm interacting protein(s). In mouse, zona pellucida glycoprotein ZP3 is believed to be the primary receptor for sperm and inducer of sperm acrosomal reaction, and its function has been attributed to the specific O-linked oligosaccharides attached to polypeptide backbone. While lots of reports have focused on the role of ZP3's oligosaccharides in fertilization, there are few concerning its polypeptide backbone. To investigate whether mZP3 polypeptide backbone is involved in sperm-egg recognition, three partially overlapping cDNA fragments, together covering entire mouse ZP3, were cloned, expressed and purified under denaturing condition. Although all three refolded proteins possess native conformation, only one derived from the carboxyl terminal showed inhibitory effect to the sperm-zona binding during in vitro fertilization. This phenomenon could not be explained by enhanced acrosomal exocytosis rate, in that the acrosomal reaction assay demonstrated its inability to induce the acrosomal reaction. Our results suggest that the carboxyl terminal of mZP3 polypeptide backbone interacts with sperm and such interaction plays a significant role in sperm-zona binding, ultimately successful fertilization.

Production of active eukaryotic proteins through bacterial expression systems: a review of the existing biotechnology strategies

Among the various expression systems employed for the over-production of proteins, bacteria still remains the favorite choice of a Protein Biochemist. However, even today, due to the lack of post-translational modification machinery in bacteria, recombinant eukaryotic protein production poses an immense challenge, which invariably leads to the production of biologically in-active protein in this host. A number of techniques are cited in the literature, which describe the conversion of inactive protein, expressed as an insoluble fraction, into a soluble and active form. Overall, we have divided these methods into three major groups: Group-I, where the factors influencing the formation of insoluble fraction are modified through a stringent control of the cellular milieu, thereby leading to the expression of recombinant protein as soluble moiety; Group-II, where protein is refolded from the inclusion bodies and thereby target protein modification is avoided; Group-III, where the target protein is engineered to achieve soluble expression through fusion protein technology. Even within the same family of proteins (e.g., tyrosine kinases), optimization of standard operating protocol (SOP) may still be required for each protein's over-production at a pilot-scale in Escherichia coli. However, once standardized, this procedure can be made amenable to the industrial production for that particular protein with minimum alterations.

Production of active eukaryotic proteins through bacterial expression systems: a review of the existing biotechnology strategies

Among the various expression systems employed for the over-production of proteins, bacteria still remains the favorite choice of a Protein Biochemist. However, even today, due to the lack of post-translational modification machinery in bacteria, recombinant eukaryotic protein production poses an immense challenge, which invariably leads to the production of biologically in-active protein in this host. A number of techniques are cited in the literature, which describe the conversion of inactive protein, expressed as an insoluble fraction, into a soluble and active form. Overall, we have divided these methods into three major groups: Group-I, where the factors influencing the formation of insoluble fraction are modified through a stringent control of the cellular milieu, thereby leading to the expression of recombinant protein as soluble moiety; Group-II, where protein is refolded from the inclusion bodies and thereby target protein modification is avoided; Group-III, where the target protein is engineered to achieve soluble expression through fusion protein technology. Even within the same family of proteins (e.g., tyrosine kinases), optimization of standard operating protocol (SOP) may still be required for each protein's over-production at a pilot-scale in Escherichia coli. However, once standardized, this procedure can be made amenable to the industrial production for that particular protein with minimum alterations.

The PLAC1-homology region of the ZP domain is sufficient for protein polymerisation

Background

Hundreds of extracellular proteins polymerise into filaments and matrices by using zona pellucida (ZP) domains. ZP domain proteins perform highly diverse functions, ranging from structural to receptorial, and mutations in their genes are responsible for a number of severe human diseases. Recently, PLAC1, Oosp1-3, Papillote and CG16798 proteins were identified that share sequence homology with the N-terminal half of the ZP domain (ZP-N), but not with its C-terminal half (ZP-C). The functional significance of this partial conservation is unknown.

Results

By exploiting a highly engineered bacterial strain, we expressed in soluble form the PLAC1-homology region of mammalian sperm receptor ZP3 as a fusion to maltose binding protein. Mass spectrometry showed that the 4 conserved Cys residues within the ZP-N moiety of the fusion protein adopt the same disulfide bond connectivity as in full-length native ZP3, indicating that it is correctly folded, and electron microscopy and biochemical analyses revealed that it assembles into filaments.

Conclusion

These findings provide a function for PLAC1-like proteins and, by showing that ZP-N is a biologically active folding unit, prompt a re-evaluation of the architecture of the ZP domain and its polymers. Furthermore, they suggest that ZP-C might play a regulatory role in the assembly of ZP domain protein complexes.

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.

Zona pellucida domain proteins

Many eukaryotic proteins share a sequence designated as the zona pellucida (ZP) domain. This structural element, present in extracellular proteins from a wide variety of organisms, from nematodes to mammals, consists of approximately 260 amino acids with eight conserved cysteine (Cys) residues and is located close to the C terminus of the polypeptide. ZP domain proteins are often glycosylated, modular structures consisting of multiple types of domains. Predictions can be made about some of the structural features of the ZP domain and ZP domain proteins. The functions of ZP domain proteins vary tremendously, from serving as structural components of egg coats, appendicularian mucous houses, and nematode dauer larvae, to serving as mechanotransducers in flies and receptors in mammals and nonmammals. Generally, ZP domain proteins are present in filaments and/or matrices, which is consistent with the role of the domain in protein polymerization. A general mechanism for assembly of ZP domain proteins has been presented. It is likely that the ZP domain plays a common role despite its presence in proteins of widely diverse functions.

Baculovirus expressed C-terminal fragment of bonnet monkey (Macaca radiata) zona pellucida glycoprotein-3 inhibits ZP3-mediated induction of acrosomal exocytosis

Zona pellucida glycoprotein-3 (ZP3) has been postulated as the primary sperm receptor in various mammalian species including bonnet monkey (Macaca radiata). However, information on the domain responsible for its binding to spermatozoa is inadequate. In the present study, bonnet monkey ZP3 (bmZP3), corresponding to amino acid (aa) residues 223-348 [bmZP3(223-348)] has been cloned and expressed using baculovirus expression system. SDS-PAGE and Western blot analysis of the purified renatured recombinant protein revealed it as a closely spaced doublet of approximately 25 kDa. Lectin-binding studies documented the presence of both O- as well as N-linked glycans. The biotinylated r-bmZP3(223-348) binds to the acrosomal region of the capacitated spermatozoa but fails to bind to the acrosome-reacted spermatozoa as investigated by immunofluorescence studies. In ELISA, nonbiotinylated r-bmZP3(223-348) and baculovirus expressed r-bmZP3, devoid of signal sequence and transmembrane-like domain [r-bmZP3(23-348)] competitively inhibit its binding to the capacitated spermatozoa. Interestingly, binding of biotinylated r-bmZP3(23-348) to the capacitated sperm is also inhibited by nonbiotinylated r-bmZP3(223-348). In contrast to r-bmZP3(23-348), r-bmZP3(223-348) failed to induce acrosomal exocytosis in the capacitated sperm. Interestingly, it competitively inhibits the acrosomal exocytosis induced by r-bmZP3(23-348). These studies, for the first time, identify a domain of ZP3 capable of binding to capacitated spermatozoa and inhibiting ZP3-mediated induction of acrosomal exocytosis furthering our understanding of mammalian fertilization.

Purification, refolding, and characterization of recombinant LHRH-T multimer

To make the native LHRH immunogenic, a multimer of LHRH interspersed with T non-B peptides (r-LHRH-d2) was expressed as recombinant protein in Escherichia coli. The expression level of the recombinant protein was around 15% of the total cellular protein and it aggregated as inclusion bodies. Inclusion bodies from the bacterial cells were isolated and purified to homogeneity. Instead of high concentrations of chaotropic agents, r-LHRH- d2 was solubilized in 50 mM citrate buffer at pH 3 containing 2 M urea. The protein was refolded by 5-fold dilution (pulsatile) with cold 10 mM citrate buffer at pH 6 in presence of 0.3 M L-arginine. Purification of r-LHRH-d2 was carried out by successive passages on CM-Sepharose column at pH 6.0 which retained extraneous proteins and pH 4.8 at which r-LHRH-d2 bound to the resin. The elution was carried out by using linear salt gradient (0.1-1 M NaCl). The overall yield of the purified r-LHRH-d2 was 40% of the initial inclusion body proteins. The purity and homogeneity were confirmed by a single homogeneous peak on analytical HPLC eluting out at 29.51 min and by single band on SDS-PAGE reactive with polyvalent anti-LHRH antibodies. Mass spectroscopic analysis indicated the protein to be of 16.6 kDa which equals the theoretically expected mass. The N-terminal amino acid analysis of r-LHRH-d2 showed the sequence which corresponded to the designed protein. The CD spectrum of the refolded r-LHRH-d2 showed that the multimer has considerable beta sheet structure like the monomeric LHRH protein.

Protein expression and refolding--a practical guide to getting the most out of inclusion bodies

The release of sequence data, particularly from a number of medically and biotechnologically important genomes, is increasing in an exponential fashion. In light of this, elucidating the structure and function of proteins, particularly in a "high throughput" manner, is an important quest. The production of recombinant proteins however is not always straightforward, with a number of proteins falling prey to low expression problems, a high susceptibility to proteolysis and the often despised production of inclusion bodies. Whilst expression as inclusion bodies can often be advantageous, their solubilization and renaturation is often a time consuming and empirical process. In this review, we aim to outline some of the more common approaches that have been applied to a variety of proteins and address issues associated with their handling.

Status of immunodiagnosis and immunocontraceptive vaccines in India

The article focuses on the Indian initiative of making kits for diagnosis of various infectious and non-infectious diseases as well as reproductive hormones and hormones in various other endocrine disorders. Indigenous diagnostic kits for the detection of various infections such as filariasis, typhoid, amebiasis, Japanese encephalitis, hepatitis, HIV, dengue, leishmaniasis, malaria, rabies, toxoplasmosis, rotavirus, and group A streptococci have been developed. Agreements to transfer the know-how of some of these leads to industries have been signed. The know-how of enzyme-linked immunosorbent assay (ELISA) for detection of hepatitis C has been successfully transferred to industry and is being commercially produced. For detection of HIV-1 and HIV-2, indigenous diagnostic kits based on three different formats, namely ELISA, Western blot and rapid test have been developed and are being commercially produced by Indian industries. The factors influencing the successful transfer of laboratory-scale diagnostic assays from academia to industry and their commercial exploitation have been discussed. Indian scientists have made seminal contributions in exploring the possibility to develop an effective and safe contraceptive vaccine to control the increasing human population of India. Achieving contraception by means of vaccine is a novel approach, which entails generation of a specific antibody response against antigens critically involved in the process of mammalian reproduction. In India, three major programs on contraceptive vaccines based on the beta-subunit of human chorionic gonadotrophin ((beta)hCG) for women, ovine follicle stimulating hormone (oFSH) for men, and riboflavin carrier protein for both males and females have been initiated. The work at the National Institute of Immunology, New Delhi on contraceptive vaccine for women, based on (beta)hCG, has demonstrated, for the first time, that it is feasible to regulate fertility by such an approach. Basic research being carried out to achieve immunocontraception by interfering at sperm-oocyte interaction level has been briefly discussed. These developments are still at the research stage. In addition to advances in the area of contraceptive vaccines, a non-steroidal contraceptive oral pill has been developed by Central Drug Research Institute, Lucknow, commercially produced by two Indian pharmaceutical companies and has been incorporated in the National Family Welfare Program. Another interesting approach for fertility regulation in male has been developed in India, which involves vas occlusion with styrene maleic anhydride (SMA) and is currently undergoing clinical trials in human subjects.

Bioprocessing of therapeutic proteins from the inclusion bodies of Escherichia coli

Escherichia coli has been most extensively used for the large-scale production of therapeutic proteins, which do not require complex glycosylation for bioactivity. In recent years tremendous progress has been made on the molecular biology, fermentation process development and protein refolding from inclusion bodies for efficient production of therapeutic proteins using E. coli. High cell density fermentation and high throughput purification of the recombinant protein from inclusion bodies of E. coli are the two major bottle necks for the cost effective production of therapeutic proteins. The aim of this review is to summarize the developments both in high cell density, high productive fermentation and inclusion body protein refolding processes using E. coli as an expression system. The first section deals with the problems of high cell density fermentation with an aim to high volumetric productivity of recombinant protein. Process engineering parameters during the expression of ovine growth hormone as inclusion body in E. coli were analyzed. Ovine growth hormone yield was improved from 60 mg L(-1) to 3.2 g L(-1) using fed-batch culture. Similar high volumetric yields were also achieved for human growth hormone and for recombinant bonnet monkey zona pellucida glycoprotein expressed as inclusion bodies in E. coli. The second section deals with purification and refolding of recombinant proteins from the inclusion bodies of E. coli. The nature of inclusion body protein, its characterization and isolation from E. coli has been discussed in detail. Different solubilization and refolding methods, which have been used to recover bioactive protein from inclusion bodies of E. coli have also been discussed. A novel inclusion body protein solubilization method, while retaining the existing native-like secondary structure of the protein and its subsequent refolding in to bioactive form, has been discussed. This inclusion body solubilization and refolding method has been applied to recover bioactive recombinant ovine growth hormone, recombinant human growth hormone and bonnet monkey zona pellucida glycoprotein from the inclusion bodies of E. coli.

Efficacy of antibodies against Escherichia coli expressed chimeric recombinant protein encompassing multiple epitopes of zona pellucida glycoproteins to inhibit in vitro human sperm-egg binding

To minimize ovarian dysfunction subsequent to immunization with zona pellucida (ZP) glycoproteins, synthetic peptides encompassing the antigenic B cell epitopes as immunogens have been proposed. In this study, attempts have been made to clone and express a recombinant chimeric protein encompassing the epitopes corresponding to bonnet monkey (Macaca radiata) ZP glycoprotein-1 (bmZP1, amino acid residues 132-147), ZP glycoprotein-2 (bmZP2, amino acid residues 86-113), and ZP glycoprotein-3 (bmZP3, amino acid residues 324-347). The above chimeric recombinant protein (r-bmZP123) was expressed as a polyhistidine fusion protein in Escherichia coli. Immunoblot with murine monoclonal antibody, MA-813, generated against recombinant bmZP1 revealed a major band of approximately 10 kDa. The r-bmZP123 was purified on nickel-nitrilotriacetic acid resin under denaturing conditions. The female rabbits immunized with purified r-bmZP123 conjugated to diphtheria toxoid (DT) generated antibodies that reacted with r-bmZP123 and DT in an ELISA. In addition, the immune sera also reacted with E. coli expressed recombinant bmZP1, bmZP2, and bmZP3. In an indirect immunofluorescence assay, the antibodies against r-bmZP123 recognized native ZP of bonnet monkey as well as human. The immune sera also inhibited, in vitro, the binding of human spermatozoa to the human zona in the hemizona assay (HZA). These studies, for the first time, demonstrate the feasibility of assembling multiple epitopes of different ZP glycoproteins as a recombinant protein that elicit antibodies which are reactive with native zona and also inhibit, in vitro, human sperm-oocyte binding.

Native zona pellucida reactivity and in-vitro effect on human sperm-egg binding with antisera against bonnet monkey ZP1 and ZP3 synthetic peptides

In mammals, zona pellucida glycoprotein-3 (ZP3) is the putative ligand for primary sperm binding and induces the acrosome reaction. Recent evidence suggests that zona pellucida glycoprotein-1 (ZP1) also play an important role, in some species, during fertilization. In order to identify synthetic peptide immunogens capable of inducing antibodies reactive with native zona and inhibiting sperm-oocyte interaction, peptide encompassing the amino acid (aa) residues 334-343 of bonnet monkey ZP3 (bmZP3) was synthesized co-linearly with a 'promiscuous' T-cell epitope of circumsporozoite protein (CSP, 378-398 aa) of Plasmodium falciparum. In addition, four peptides corresponding to bonnet monkey ZP1 (bmZP1((58-79 aa)), bmZP1((136-153 aa)), bmZP1((212-228 aa)) and bmZP1((251-273 aa))) were synthesized. The synthetic peptides corresponding to bmZP1 were conjugated with diphtheria toxoid. Immunization of female BALB/cJ mice with the above conjugates and CSP-bmZP3((334-343 aa)) peptide led to the generation of an adequate antibody response against the respective zona peptide. Antibodies against bmZP1((251-273 aa)) and CSP-bmZP3((334-343 aa)) recognized bonnet monkey and human zona pellucida in an indirect immunofluorescence assay. Further, these antibodies when tested independently or in combination also significantly inhibited the binding of human spermatozoa to zona pellucida in a hemizona assay. These studies will further help in the design of synthetic peptide immunogens comprising of multiple B cell epitope from different zona proteins for better immunocontraceptive efficacy.

Primate recombinant zona pellucida proteins expressed in Escherichia coli bind to spermatozoa

To delineate the role of individual zona pellucida (ZP) glycoproteins during sperm-oocyte interaction, bonnet monkey (bm; Macaca radiata) ZPA (bmZPA), ZPB (bmZPB), and ZPC (bmZPC) have been cloned without native signal sequence and transmembrane-like domain, and expressed in Escherichia coli. Recombinant proteins have been purified from the inclusion bodies in presence of low concentration of chaotropic agent (2 M urea) and high pH (pH 12), and subsequently refolded in presence of oxidized and reduced glutathione. Binding of the recombinant refolded zona proteins to bonnet monkey spermatozoa in an indirect immunofluorescence assay revealed that recombinant bmZPC binds to the head region of the capacitated spermatozoa but does not bind to the acrosome reacted spermatozoa. Recombinant bmZPB binds to the principal segment of the acrosomal cap of capacitated bonnet monkey spermatozoa. After induction of acrosome reaction by calcium ionophore A23187, the binding of recombinant bmZPB shifts to the equator, post-acrosome and midpiece of the spermatozoa. bmZPA binds to the principal segment of capacitated spermatozoa but the binding shifts to the equatorial segment, tip of the inner acrosomal membrane and midpiece in acrosome reacted spermatozoa. These studies suggest that polypeptide backbone is sufficient for the binding of ZPA, ZPB and ZPC to spermatozoa in non-human primates. Further studies with recombinant glycosylated zona proteins will help in delineating the role of carbohydrate moieties for higher affinity binding of the ligand to spermatozoa and subsequent signal transduction pathways.