Rapana thomasiana hemocyanin (RtH): dissociation and reassociation behavior of two isoforms, RtH1 and RtH2

Antitumor Properties of Epitope-Specific Engineered Vaccine in Murine Model of Melanoma

Finding new effective compounds of natural origin for composing anti-tumor vaccines is one of the main goals of antitumor research. Promising anti-cancer agents are the gastropodan hemocyanins-multimeric copper-containing glycoproteins used so far for therapy of different tumors. The properties of hemocyanins isolated from the marine snail Rapana thomasiana (RtH) and the terrestrial snail Helix aspersa (HaH) upon their use as carrier-proteins in conjugated vaccines, containing ganglioside mimotope GD3P4 peptide, were studied in the developed murine melanoma model. Murine melanoma cell line B16F10 was used for solid tumor establishment in C57BL/6 mice using various schemes of therapy. Protein engineering, flow cytometry, and cytotoxicity assays were also performed. The administration of the protein-engineered vaccines RtH-GD3P4 or HaH-GD3P4 under the three different regimens of therapy in the B16F10 murine melanoma model suppressed tumor growth, decreased tumor incidence, and prolonged the survival of treated animals. The immunization of experimental mice induced an infiltration of immunocompetent cells into the tumors and generated cytotoxic tumor-specific T cells in the spleen. The treatment also generates significantly higher levels of tumor-infiltrated M1 macrophages, compared to untreated tumor-bearing control mice. This study demonstrated a promising approach for cancer therapy having potential applications for cancer vaccine research.

Intensive therapy with gastropodan hemocyanins increases their antitumor properties in murine model of colon carcinoma

Various natural compounds have been tested as anticancer therapeutics in clinical trials. Most promising direction for antitumor therapy is the use of substances which enhance the immune system response stimulating tumor-specific lymphocytes. Hemocyanins are large extracellular oxygen transport glycoproteins isolated from different arthropod and mollusk species which exhibit strong anticancer properties. Immunized in mammals they trigger Th1 immune response that promotes unspecific stimulation and adjuvant activity in experimental therapeutic vaccines for cancer and antibody development. In the present study we used two hemocyanins - one isolated from marine snail Rapana thomasiana (RtH) and another one, from the terrestrial snail Helix pomatia (HpH) which have been investigated by using different administration schedules (intensive and mild) in murine model of colon carcinoma. The treatment with RtH and HpH generated high levels of antitumor IgG antibodies, antibody-producing plasma cells and tumor-specific CTLs, stimulated secretion of proinflammatory cytokines, suppressed the manifestation of carcinoma symptoms as tumor growth and size, and prolonged the life span of treated mice. Our results showed a significant anti-cancer effect of RtH and HpH hemocyanins on a murine model of colon carcinoma with promising potential for immunotherapy in various schemes of administration based on cross-reactive tumor-associated epitopes.

Anti-cancer properties of gastropodan hemocyanins in murine model of colon carcinoma

BACKGROUND

Various immunotherapeutic approaches have been used for the treatment of cancer. A number of natural compounds are designed to repair, stimulate, or enhance the immune system response. Among them are the hemocyanins (Hcs) - extracellular copper proteins isolated from different arthropod and mollusc species. Hcs are oxygen transporter molecules and normally are freely dissolved in the hemolymph of these animals. Hemocyanins are very promising class of anti-cancer therapeutics due to their immunogenic properties and the absence of toxicity or side effects. KLH (Megathura crenulata hemocyanin) is the most studied molecule of this group setting a standard for natural carrier protein for small molecules and has been used in anti-tumor clinical trials.

RESULTS

The Hcs isolated from marine snail Rapana thomasiana (RtH) and the terrestrial snail Helix pomatia (HpH) express strong in vivo anti-cancer and anti-proliferative effects in the developed by us murine model of colon carcinoma. The immunization with RtH and HpH prolonged the survival of treated animals, improve humoral anti-cancer response and moderate the manifestation of C-26 carcinoma symptoms as tumor growth, splenomegaly and lung metastasis appearance.

CONCLUSION

Hemocyanins are used so far for therapy of superficial bladder cancer and murine melanoma models. Our findings demonstrate a potential anti-cancer effect of hemocyanins on a murine model of colon carcinoma suggesting their use for immunotherapy of different types of cancer.

Marine gastropod hemocyanins as adjuvants of non-conjugated bacterial and viral proteins

Killed viral vaccines and bacterial toxoids are weakly immunogenic. Numerous compounds are under evaluation as immunological adjuvants and peptide-carriers to improve the immune response. The hemocyanins, giant extracellular copper proteins in the blood of many mollusks, are widely used as immune stimulants. In the present study we investigated the adjuvant properties of hemocyanins isolated from marine gastropods Rapana thomasiana and Megathura crenulata. An immunization with Influenza vaccine or tetanus toxoid combined with Rapana thomasiana hemocyanin (RtH) and Keyhole limpet hemocyanin (KLH) in mice induced an anti-influenza cytotoxic response lasting at least 5 months and an antibody response to viral proteins. The IgG antibody response to the tetanus toxoid (TT) combined with RtH or KLH was comparable to the response of the toxoid in complete Freund's adjuvant. The results obtained demonstrate that the both hemocyanins are acceptable as potential bio-adjuvants for subunit vaccines.

Conformational stabilization at the active site of molluskan (Rapana thomasiana) hemocyanin by a cysteine-histidine thioether bridge A study by mass spectrometry and molecular modeling

In some type-3 copper proteins (molluskan hemocyanin, catechol oxidase and fungal tyrosinase) one of the histidine residues, liganding the Cu(A) atom of the dinuclear copper active site, is covalently linked to a cysteine residue by a thioether bridge. The purpose of this study was to disclose the function of this bridge. Mass spectral analysis of a peptide, isolated from Rapana thomasiana (gastropodan mollusk) hemocyanin, indicated a stabilization of the peptide structure in the region of the bridge. Molecular modeling of three thioether containing type-3 copper proteins using the dead-end elimination method showed that the concerned histidine would be very flexible if not linked to the cysteine. Also, the side chain orientation of the histidine is rather exceptional, as evidenced by statistical data from the protein databank. It is suggested that the role of the bridge is to fix the histidine in an orientation that is optimal for coordination of the Cu(A) atom.

Rapana thomasiana hemocyanin (RtH): comparison of the two isoforms, RtH1 and RtH2, at 19A and 16A resolution

Three-dimensional (3D) reconstructions of the two 8.4 MDa Rapana thomasiana hemocyanin isoforms, RtH1 and RtH2, have been obtained by cryoelectron microscopy of molecules embedded in vitreous ice and single particle image processing. The final 3D structures of the RtH1 and RtH2 didecamers at 19 A and 16 A resolution, respectively, are very similar to earlier reconstructions of gastropodan hemocyanins, revealing structural features such as the obliquely oriented subunits, the five- and two-fold symmetrical axes. Three new interactions are defined; two of them connecting the arch and the wall while the third is formed between the collar and the wall. The collar-wall connection and one of the arch-wall connections are positioned between two individual subunit dimers, while the second arch-wall connection is located between two subunits within the subunit dimer. All three interactions establish connections to the first tier of the wall. Furthermore, for each interaction we have allocated two first tier functional units most likely involved in forming the connections.

Glycosylation of Rapana thomasiana hemocyanin. Comparison with other prosobranch (gastropod) hemocyanins

The carbohydrate content and composition of hemocyanins (Hcs) of three prosobranchs (gastropods), Rapana thomasiana, Megathura crenulata and Haliotis tuberculata, were compared. The analyses were performed by gas-liquid chromatography after methanolysis, re-N-acetylation and trimethylsilylation. The two structural subunits of R. thomasiana Hc, RtH1 and RtH2, both showed 2.6% (w/w) carbohydrate content with very similar monosaccharide composition, indicative for N-glycosylation. The two isoforms of M. crenulata Hc (KLH), KLH1 and KLH2, on the other hand, definitely differed in glycosylation: KLH2 (3.4% carbohydrate, w/w) comprised relatively less mannose and more N-acetylgalactosamine than KLH1 (3.0% carbohydrate, w/w), in agreement with the fact that O-glycosylation has been observed in a functional unit (FU) of KLH2. For the Hc of the abalone H. tuberculata, with 4.5% (w/w) carbohydrate, appreciable amounts of 3-O-methyl-d-mannose and 3-O-methyl-d-galactose were detected, showing that the occurrence of methylated sugars is not restricted to the Hcs of pulmonates. From the structural subunit RtH2 of Rapana Hc the FUs RtH2-b and RtH2-d were isolated. On the basis of amino acid sequence analysis and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) of the respective native and PNGase-F-treated glycopeptides, one N-glycosylation site was found for each FU. This site was located at Asn-405 for RtH2-b and at Asn-394 for RtH2-d; the carbohydrate moiety corresponded to GlcNAc2Man6 and GlcNAc2Man5, respectively. A comparison was made with the N-glycosylation sites of other FUs of Rapana Hc.

Differential scanning calorimetry of the irreversible denaturation of Rapana thomasiana (marine snail, Gastropod) hemocyanin

The thermal denaturation of the hemocyanin from gastropod Rapana thomasiana (RtH) at neutral pH was studied by means of differential scanning calorimetry (DSC). The denaturation was completely irreversible as judged by the absence of any endotherm on rescanning of previously scanned samples. Two transitions, with apparent transition temperatures (T(m)) at 83 and 90 degrees C, were detected by DSC using buffer 20 mM MOPS, containing 0.1 M NaCl, 5 mM CaCl(2) and 5 mM MgCl(2), pH 7.2. Both T(m) were dependent on the scanning rate, suggesting that the thermal denaturation of RtH is a kinetically controlled process. The activation energy (E(A)) of 597+/-20 kJ mol(-1) was determined for the main transition (at 83 degrees C). E(A) for the second transition was 615+/-25 kJ mol(-1). The T(m) and Delta H(cal) values for the thermal denaturation of RtH were found to be independent of the protein concentration, signifying that the dissociation of the protein into monomers does not take place before the rate-determining state of the process of thermal unfolding.

Conformational states of the Rapana thomasiana hemocyanin and its substructures studied by dynamic light scattering and time-resolved fluorescence spectroscopy

Hemocyanins are dioxygen-transporting proteins freely dissolved in the hemolymph of mollusks and arthropods. Dynamic light scattering and time-resolved fluorescence measurements show that the oxygenated and apo-forms of the Rapana thomasiana hemocyanin, its structural subunits RtH1 and RtH2, and those of the functional unit RtH2e, exist in different conformations. The oxygenated respiratory proteins are less compact and more asymmetric than the respective apo-forms. Different conformational states were also observed for the R. thomasiana hemocyanin in the absence and presence of an allosteric regulator. The results are in agreement with a molecular mechanism for cooperative dioxygen binding in molluscan hemocyanins including transfer of conformational changes from one functional unit to another.

cDNA Sequence, Protein Structure, and Evolution of the Single Hemocyanin from Aplysia californica, an Opisthobranch Gastropod

By protein immunobiochemistry and cDNA sequencing, we have found only a single hemocyanin polypeptide in an opisthobranch gastropod, the sea hare Aplysia californica, which contrasts with previously studied prosobranch gastropods, which express two distinct isoforms of this extracellular respiratory protein. We have cloned and sequenced the cDNA encoding the complete polypeptide of Aplysia californica hemocyanin (AcH). The cDNA comprises 11,433 bp, encompassing a 5'UTR of 77 bp, a 3'UTR of 1057 bp, and an open reading frame for a signal peptide of 20 amino acids plus a polypeptide of 3412 amino acids (Mr ca. 387 kDa). This polypeptide is the subunit of the cylindrical native hemocyanin (Mr ca. 8 MDa). It comprises eight different functional units (FUs: a, b, c, d, e, f, g, h) that have been identified immunobiochemically after limited proteolysis of AcH purified from the hemolymph. Each FU shows a highly conserved copper-A and copper-B site for reversible oxygen binding. FU AcH-h carries a specific C-terminal extension of ca. 100 amino acids that include two cysteines that may be utilized for disulfide bridge formation. Potential N-glycosylation sites are present in six FUs but lacking in AcH-b and AcH-c. On the basis of multiple sequence alignments, phylogenetic trees and a statistically firm molecular clock were calculated. The latter suggests that the last common ancestor of Haliotis and Aplysia lived 373+/-47 million years ago, in convincing agreement with fossil records from the early Devonian. However, the gene duplication yielding the two distinct hemocyanin isoforms found today in Haliotis tuberculata occurred 343+/-43 million years ago.

Hemocyanin of the Molluscan Concholepas concholepas Exhibits an Unusual Heterodecameric Array of Subunits

We describe here the structure of the hemocyanin from the Chilean gastropod Concholepas concholepas (CCH), emphasizing some attributes that make it interesting among molluscan hemocyanins. CCH exhibits a predominant didecameric structure as revealed by electron microscopy and a size of 8 MDa by gel filtration, and, in contrast with other mollusc hemocyanins, its stabilization does not require additional Ca(2+) and/or Mg(2+) in the medium. Polyacrylamide gel electrophoresis studies, analyses by a MonoQ FPLC column, and Western blots with specific monoclonal antibodies showed that CCH is made by two subunits noncovalently linked, named CCH-A and CCH-B, with molecular masses of 405 and 350 kDa, respectively. Interestingly, one of the subunits undergoes changes within the macromolecule; we demonstrated that CCH-A has an autocleavage site that under reducing conditions is cleaved to yield two polypeptides, CCH-A1 (300 kDa) and CCH-A2 (108 kDa), whereas CCH-B remains unchanged. The CCH-A nick occurs at 4 degrees C, increases at 37 degrees C, and is not inhibited by the addition of protease inhibitors and/or divalent cations. Since the CCH structure is a heterodimer, we investigated whether subunits would be either intermingled, forming heterodecamers, or assembled as two homogeneous decamers. Light scattering and electron microscope studies of the in vitro reassociation of purified CCH subunits demonstrated that the sole addition of Mg(2+) is needed for its reassembly into the native decameric molecule; no homodecamer reorganization was found with either CCH-A or CCH-B subunits alone. Our evidence showed that C. concholepas hemocyanin is an unusual example of heterodecameric organization.

Oligomeric stability of Rapana venosa hemocyanin (RvH) and its structural subunits

The two structural subunits RvH1 and RvH2 were separated after overnight dialysis of Rapana venosa Hc against 130 mM Gly/NaOH buffer, pH 9.6, on an ion exchange column Hiload 26/10 Sepharose Q using a fast performance liquid chromatography (FPLC) system. The reassociation characteristics of these two RvH isoforms and the native molecule were studied in buffers with different pH values and concentrations of Ca(2+) and Mg(2+). Reassociation of mixed RvH subunits was performed over a period of several days using a stabilizing buffer (SB) of pH 7.0 containing different concentrations of Ca(2+) and Mg(2+) ions. After 2 days of dialysis, an RvH subunit mixture of didecamers and multidecamers was observed in the presence of 100 mM CaCl(2) and MgCl(2), though RvH1 and RvH2 are biochemically and immunologically different and have also different dissociation properties. The reassociation, performed at pH 9.6 with 2 mM CaCl(2) and MgCl(2) at 4 degrees C over a period of one to several weeks, led to the formation of decameric oligomers, while didecamers formed predominantly in the SB at pH 7.0. Higher concentrations of calcium and magnesium ions led to a more rapid reassociation of RvH1 resulting in long stable multidecamers and helical tubules, which were stable and slowly dissociated into shorter multidecamers and decamers at higher pH values. The reassociation of the RvH2 structural subunit in the same buffers processed slowly and yielded didecamers, shorter tubule polymers and long multidecamers which are less stable at higher pH values. The stability of RvH isoforms under varying ionic conditions is compared with the stability of keyhole limpet (KLH, Megathura crenulata) hemocyanin (KLH) and Haliotis tuberculata hemocyanin (HtH) isoforms. The process of dissociation and reassociation is connected with changes of the fluorescence intensity at 600 nm, which can be explained by differences in opalescence of the solutions of these two isoforms. The solutions of longer tubule polymers and multidecamers of RvH1 show a higher opalescence compared to the solutions of shorter helical tubules and multidecamers of RvH2.