Purification and characterization of a ribonuclease from Aspergillus giganteus IFO 5818, the gigantin. Immunological and enzymic comparison with alphasarcin

A protein has been isolated from a culture medium of Aspergillus giganteus IFO 5818 (gigantin) and purified by ion-exchange chromatography successively on DEAE-cellulose and carboxymethyl-cellulose, and gel-filtration chromatography on Biogel P10. With a high purity, gigantin was found to be a non-glycosylated basic protein with a relative molecular mass of 17000 +/- 200 determined in PAGE/SDS. Gigantin was able to digest the synthetic homopolymers of nucleic acids poly(A), poly(I), poly(C) and poly(U). The catalytic action has an optimal pH around 7.0, an optimal temperature at 45-55 degrees C and can be inhibited by cations. Gigantin activity, analyzed as its capacity to hydrolyze RNA from yeast, was comparable to that of alphasarcin, a similar biochemical protein produced by the strain A. giganteus MDH 18894. A study of the substrate specificity for alphasarcin indicated a preference for poly(A) and poly(I), while gigantin had greater activity on poly(C) and poly(U). The cross reaction of gigantin with a rabbit antiserum to alphasarcin suggests a high sequence similarity between both proteins. However, gigantin is immunologically distinguishable from alphasarcin as alphasarcin antiserum detects epitopes in alphasarcin that are not present in gigantin.

A toxic protein from Bryonia dioica Jacq. fruits: the brydiofin

A toxic protein isolated from Bryonia dioica Jacq. fruits is described. The fruit extract, obtained in phosphate buffer saline, in mild conditions, showed a strongly toxic activity after intraperitoneal injection of 0.4 mg per Balb/c mouse that was killed in eighteen minutes. The extract, filtered through a Bio-Gel P-60 column, presented a main peak that showed similar toxicity. When the material from this peak was analyzed in polyacrylamide slab gels, a single band corresponding to a molecular weight of about 66,000 was observed. The lethal effect of B. dioica fruit could be attributed to a protein that we called Brydiofin. The extracts from roots and leaves that did not present this toxicity showed no band in this molecular weight region.

Fractionation of the ribosome inactivating protein preparations with triazine dyes

Aspergillins are ribosome-inactivating proteins (RIPs), isolated from several strains of Aspergillus. The interaction between Cibacron Blue F3GA and two members of this family, alpha sarcin and mitogillin, and other RIPs of type I, was studied. Alpha sarcin retention depended on pH and ionic strength. By chromatography on Affi-Gel Blue in mild experimental conditions, mitogillin and PAP-I did not interact with the dye, whereas 40% of alpha sarcin and 70-90% of briodin, RTA and gelonin were recovered in the bound fraction. In all cases, the major fraction showed a higher toxicity level in protein synthesis inhibition assays. The unbound alpha sarcin, conjugated with the anti-ovarian carcinoma monoclonal antibody MOv17, showed on OVCA 432 a cytotoxicity which was 900 times higher than that exerted by the alpha sarcin alone.

The Aspergillus toxin restriction is a suitable cytotoxic agent for generation of immunoconjugates with monoclonal antibodies directed against human carcinoma cells

The protein toxin restriction, isolated from the mould Aspergillus restrictus, inactivates protein synthesis in eukaryotic cells by blocking the ribosome elongation cycle. This protein acts as a specific nuclease that cuts off a small fragment from the 28-S rRNA. Biochemical and biological characterization of this toxin indicated that it is a non-glycosylated polypeptide of Mr 16836, exhibiting in cell-free systems a protein synthesis inhibition capacity similar to that of the ricin A chain. This polypeptide seemed unable to penetrate most of the cancer cell lines tested, as measured by its low in vitro cytotoxicity. In addition in vivo studies in BALB/c mice demonstrated that restriction toxicity was very low and that in rabbits, after intravenous injection 15% of the toxin was still present in the blood stream 24 h later. After derivatization with N-succinimidyl 3-(2-pyridyldithio)propionate and reduction by dithiothreitol, the restrictocin maintained its protein synthesis inhibitory activity, as assayed in a cell-free system. This derivatized toxin was then coupled to monoclonal antibodies (MBr1, MLuC1, MLuC2, MOv17, MOv18, MOv19) which exhibited a restricted spectrum of reactivity against human carcinomas. The biochemical and biological characterization of the immunoconjugates indicated that (a) when restrictocin was coupled to monoclonal antibodies with an average molar ratio of about 2, the immunoconjugates maintained the binding activity of the antibody and protein synthesis inhibition activity of the toxin; (b) four immunoconjugates were tested for cytotoxicity and three of them obtained with the MBr1, MLuC1 and MOv17 monoclonal antibodies exhibited a good level of cytotoxicity for relevant target cells and low or no toxicity for the irrelevant cell lines. The MLuC2 monoclonal antibody which gave rise to a completely ineffective immunoconjugate, induced internalization of less than one tenth of the antigenic sites whereas the MBr1, MLuC1 and MOv17 monoclonal antibodies exhibited about one third of the antigenic sites interanalized. From these data it is concluded that, providing an appropriate target antigen and coupling procedure are selected, restrictocin can be considered a suitable toxin for immunoconjugate generation.

Immunoconjugate generation between the ribosome inactivating protein restrictocin and an anti-human breast carcinoma MAB

In the perspective of therapeutic approaches the monoclonal antibody, MBrl, with a quite restricted spectrum of reactivity for human breast carcinoma, was coupled to restrictocin (Res), a ribosome inactivating protein produced by Aspergillus restrictus. In a cell-free system this toxin was found to have an activity comparable to that of other plant toxins, but its in vitro toxicity was shown to be low on different cell lines. Three batches of MBr1-Res conjugate were prepared and their specificity, efficiency, and maximum level of cytotoxicity were analyzed on the cell line MCF-7 expressing the relevant antigen, on several irrelevant tumor cell lines, and on normal cells. Conjugates were from 600 to 1500 times more efficient than the uncoupled derivatized Res towards MCF-7 cells and were completely ineffective on the other target cells. The antigen-driven cytotoxicity was confirmed by the nontoxicity of an irrelevant conjugate on MCF-7 cells. The cytotoxic efficiency of MBr1-Res was low when compared to the binding level of MBr1 at the same concentration and a portion of treated cells (from 10% to 30%) survived the treatment. The heterogeneity of expression of the relevant antigen, together with its only partial internalization, could account for these limitations. The lysosomotropic agent ammonium chloride and the carboxylic ionophore monensin were tested as potentiating agents but in both cases the cytotoxicity remained unmodified. A neutralization assay performed on a xenogenic model indicated that the MBr1-Res conjugate was capable of reducing the tumor take. These data indicate the possibility of using the Res to prepare a reproducible and highly selective breast cancer conjugate. However, there are still a number of problems which must first be solved before we can consider its clinical application.

Alternative mechanism of protein A-immunoglobulin interaction the VH-associated reactivity of a monoclonal human IgM

The immunoglobulin site(s) that mediates the alternative mechanism of interaction between immunoglobulins and staphylococcal protein A (SpA) was studied by using a monoclonal human IgM. Several IgM fragments were tested for their inhibitory effect in a competitive binding assay of 125I-IgM to SpA. Only those fragments containing Fab mu pieces showed some inhibitory activity. The reactivity of the Fab mu region was retained in some of its subfragments, such as Fv or the VH domain, unlike isolated light chains or VL domains. Furthermore, antibodies specific for the VH domain completely inhibited the SpA-IgM interaction. These results indicate that the alternative SpA-binding site of IgM is located in VH regions.

Alternative mechanism of protein A-immunoglobulin interaction the VH-associated reactivity of a monoclonal human IgM

The immunoglobulin site(s) that mediates the alternative mechanism of interaction between immunoglobulins and staphylococcal protein A (SpA) was studied by using a monoclonal human IgM. Several IgM fragments were tested for their inhibitory effect in a competitive binding assay of 125I-IgM to SpA. Only those fragments containing Fab mu pieces showed some inhibitory activity. The reactivity of the Fab mu region was retained in some of its subfragments, such as Fv or the VH domain, unlike isolated light chains or VL domains. Furthermore, antibodies specific for the VH domain completely inhibited the SpA-IgM interaction. These results indicate that the alternative SpA-binding site of IgM is located in VH regions.

Use of human IgM derived fragments to study structures responsible for protein A-reactivity

The protein A-binding site of human IgM was studied by affinity chromatography on SpA-Sepharose using fragments derived from a human monoclonal SpA-reactive IgM, Iz. Neither Fabmu nor (Fc) 5mu fragments were retained on the column but IgM reactivity was unaffected by thermic treatment during proteolysis. Products intermediate between IgM and (Fc) 5mu fragments produced during shorter proteolysis showed a reactivity related to their content in Fabmu regions. On the other hand mild reduction of IgM Iz to monomeric subunits results in a dramatic loss of SpA-affinity. However these subunits, like F(ab') 2mu but unlike Fab'mu fragments, showed a significant interaction with the column. Thus, the principal requirement for SpA reactivity with IgM Iz seems to be related to the presence of Fabmu regions in a polymeric state resembling native IgM.

Binding of human immunoglobulin M to Staphylococcus aureus bearing protein A

Human immunoglobulin M binds to protein A-bearing Staphylococcus aureus. This binding is specific for protein A since it is inhibited by rabbit Fab against Staphylococcal protein A. Analysis of the IgM binding data gives an apparent KD of 0.94 nM and a maximum capacity of approximately 2 X 10(3) binding sites of IgM per bacteria.

Human immunoglobulin M purification by affinity chromatography on protein A--Sepharose

A method is described for preparing IgM from normal serum in two chromatographic steps. A gel filtration column gives a macroglobulin peak containing the IgM, purified by affinity chromatography on protein A--Sepharose. Immunoglobulin recovery is around 50%.

Studies of the IgM and IgA contamination obtained by eluting IgG from protein A-Sepharose column with pH steps

The IgG fraction obtained from pooled human plasma by eluting a protein A column with a buffer at pH 2.5 was contaminated with approximately 30% of the IgM originally present in the sample. Both the IgM and the IgA contamination can be reduced and the IgG recovery maintained at 90% of the bound IgG when elution of the column is performed at pH 4.0

Comparative study between prokaryotes and eukaryotes by chemical iodination of ribosomal proteins

Escherichia coli and Saccharomyces cerevisiae ribosomal proteins were chemically iodinated with 125I by chloramine T under conditions in which the proteins were denatured. The labelled proteins were subsequently separated by two-dimensional gel electrophoresis with an excess of untreated ribosomal proteins from the same species. The iodination did not change the electrophoretic mobility of the proteins as shown by the pattern of spots in the stained gel slabs and their autoradiography. The 125I radioactivity incorporated in the proteins was estimated by cutting out the gel spots from the two-dimensional electrophoresis gel slabs. The highest content of 125I was found in the ribosomal proteins L2, L11, L13, L20/S12, S4 and S9 from E. coli, and L2/L3, L4/L6/S7, L5, L19/L20, L22/S17, L29/S27, L35/L37 and S14/S15 from S. cerevisiae. Comparisons between the electrophoretic patterns of E. coli and S. cerevisiae ribosomal proteins were carried out by coelectrophoresis of labelled and unlabelled proteins from both species. E. coli ribosomal proteins L5, L11, L20, S2, S3 and S15/S16 were found to overlap with L15, L11/L16, L36/L37, S3, S10 and S33 from S. cerevisiae, respectively. Similar coelectrophoresis of E. coli 125I-labelled proteins with unlabelled rat liver and wheat germ ribosomal proteins showed the former to overlap with proteins L1, L11, L14, L16, L19, L20 and the latter with L2, L5, L6, L15, L17 from E. coli.

Comparative studies of sheep immunoglobulins IgG1 and IgG2: amino acid sequence of carboxy-terminal cyanogen bromide fragments from their heavy chains

Sheep immunoglobulin IgG1 and immunoglobulin IgG2 heavy chains were treated with cyanogen bromide. The fractions from the C-terminal end of the heavy chains were isolated and purified, and the amino acid sequences gamma1 and gamma2 heavy chains had the identical sequence: Met-His-Glx-Ala-Leu-His-Asx-His-Tyr-Thr-Glx-Lys-Ser-Ile-Ser-Lys-Pro-Pro-Gly. Comparison with the C-terminal peptides of other species, reported in the literature, suggests that the subclasses are the results of recent evolutionary processes. Residues at position 4 from the C-terminus may be phylogenetically related.