Pierrette Maes

Molecular characterization of a dense granule antigen (Gra 2) associated with the network of the parasitophorous vacuole in Toxoplasma gondii

The monoclonal antibody (mAb) TG17.179 recognizes an excreted-secreted antigen (ESA) of 28.5 kDa named Gra 2, which is stored in the dense granules of Toxoplasma cells and secreted into the parasitophorous vacuole after host cell invasion. Screening of an expression cDNA library with TG17.179 led to the isolation of several clones, the longest one (clone L) being of 1030 bp. Clone L cDNA was found to be homologous to a previously described composite cDNA encoding a P28 protein of Toxoplasma gondii. Characterization of one genomic clone indicates that the complete GRA 2 gene is about 1.3 kb in length, including an intron of 241 bp. Northern blot and primer extension analyses confirmed the size of the mature messenger (1.1 kb). Amino acid partial sequencing of the native antigen purified by HPLC and metabolic radiolabelings of ESAs perfectly matched the primary amino acid structure deduced from the clone L cDNA. This primary translation product consists of an 185 amino acid polypeptide (19.8 kDa) including a 23 amino acid signal sequence. The presence of many serine and threonine residues may indicate an O-glycosylation. The predicted mature polypeptide shows an internal helical domain with 2 amphipathic alpha-helices. These might be involved in the association of Gra 2 with the membranous network within the parasitophorous vacuole.

The complete amino acid sequence of bovine milk angiogenin

The amino acid sequence of angiogenin isolated from bovine milk was deduced by gas‐phase sequencing of the protein and its fragments. The protein contains 125 residues and has a calculated molecular mass of 14 577 Da. The sequence is highly homologous (65% identity) to the sequence of human angiogenin, most of the differences being the result of conservative replacements. Like human angiogenin, the bovine protein is also homologous to bovine pancreatic RNase A (34% identity) and the three major active site residues known to be involved in the catalytic process, His‐14, Lys‐41 and His‐115, are conserved. When tested against conventional substrates for RNase A activity, bovine angiogenin displays the same selective ribonucleolytic activity as human angiogenin. The sequence of bovine angiogenin contains the cell recognition tripeptide Arg‐Gly‐Asp which is not present in the human protein.

Protective immunity in the rat model of congenital toxoplasmosis and the potential of excreted-secreted antigens as vaccine components

Toxoplasma infection is a major cause of severe foetal pathology both in humans and in domestic animals, particularly sheep. We have previously reported the development of an experimental model to study congenital toxoplasmosis in the rat. Here we demonstrate that, as in humans, total protection against congenital toxoplasmosis can be achieved regardless of the strain of Toxoplasma gondii used to infect rats, or when initial and challenge infections were carried out with different strains. Chronic infection is associated with a highly specific immunity that involves both B‐and T‐cell responses beginning at day 10 postinfection. The antibody isotype analysis revealed that whereas immunoglobulin (Ig)G2b is the major elicited isotype, no IgG1 antibodies are detected. T cell proliferation was assayed using crude Toxoplasma extracts or excretory‐secretory antigens (ESA). The analysis of T cell supernatants showed the specific secretion of both interleukin‐2 and interferon‐γ by activated T cells. Immunization of rats before pregnancy with either crude Toxoplasma extracts or with ESA elicited a B cell response that included antibodies of the IgG1 isotype and conferred on the newborns high levels of protection. Preliminary experiments of immunization using two HPLC‐purified ESA, GRA2 and GRA5, conferred, a significant protection although to a lesser extent. This experimental model represents an attractive model for the identification of future vaccine candidates against congenital toxoplasmosis.

Intramolecular mapping of Plasmodium falciparum P126 proteolytic fragments by N-terminal amino acid sequencing.

Protein P126 (also called P140, P113, SERA, SERP1) is a major parasitophorous vacuole antigen of Plasmodium falciparum. This protein is processed upon merozoite release into 2 fragments of 73 kDa (P73) and 50 kDa (P50), which are found in the culture medium. P73 is composed of 2 polypeptides of 47 and 18 kDa linked by disulfide bridges. In the presence of leupeptin, an inhibitor of serine and cysteine proteases which inhibits merozoite release, a 56-kDa intermediate product (P56) is recovered in the culture medium instead of P50. In order to map these proteolytic fragments on the 126-kDa precursor, we purified them from Plasmodium falciparum culture medium by immunoadsorption, SDS-electrophoresis and Western blotting on PVDF membrane and determined the N termini of P126, P73 (P47 and P18), P50 and P56. Comparison of these sequences with the amino acid sequence deduced from the P126 gene allowed the mapping of the different fragments on the precursor. P47 was at the N-terminal and P18 at the C-terminal end of P126. P56 and P50 had the same N-termini and were located in the middle of P126. This latter result indicates that the proteolysis of P56-P50 occurs at the C-terminus of P56. The peptide bonds cleaved by leupeptin-insensitive activities are Glu-Thr and Gln-Asp; C-terminal sequencing of P50 will be needed to identify the leupeptin-sensitive cleavage site.

Charybdotoxin blocks dendrotoxin-sensitive voltage-activated K+ channels.

Charybdotoxin, a short scorpion venom neurotoxin, which was thought to be specific for the blockade of Ca2+‐activated K+ channels also blocks a class of voltage‐sensitive K+ channels that are known to be the target of other peptide neurotoxins from snake and bee venoms such as dendrotoxin and MCD peptide. Charybdotoxin also inhibits 125‐dendrotoxin and 125I‐MCD peptide binding to their receptors. All these effects are observed with an IC50 of about 30 nM.

Characterization of a hyaluronic acid-binding protein from sheep brain comparison with human brain hyaluronectin.

1. A hyaluronic acid (HA)-binding glycoprotein from sheep brain was characterized. 2. The specific affinity for HA was shown in vitro by high performance liquid chromatography, polyacrylamide gel electrophoresis and ELISA methods. 3. The KD for high molecular weight HA was 5.4 10(-9) M at 37 degrees C and lower than 10(-10) M at 4 degrees C. 4. No link protein was found and HA molecules could bind up to 10 times their weight of the glycoprotein. 5. The specific site for interaction was the HA-derived decasaccharide HA10. 6. The protein is composed of one polypeptidic chain. Tryptophan and lysine play a prominent role in the conformation of the binding site to HA. 7. Enzyme analysis indicated that the protein different forms are due to differences in glycosylation and that N- and O-linkages coexist in the molecules. 8. Immunohistochemistry localized the glycoprotein at the nodes of Ranvier and at the periphery of neurons. The perineuronal labeling was seen around all neurons studied in the cerebellum whereas it was almost undetectable in the cerebral hemispheres. 9. HA is not saturated by hyaluronectin (HN) in the sheep nervous system. 10. The glycoprotein is largely similar to human brain HN, and different from the hyaluronate-binding protein characterized in the cartilage.

Cloning and sequence analysis of the gene encoding an NADP-dependent alcohol dehydrogenase in Mycobacterium bovis BCG

The nucleotide sequence of a 1619-bp fragment of Mycobacterium bovis BCG containing the gene that encodes an alcohol dehydrogenase (ADH) has been determined. The M(r) calculated from the deduced amino acid (aa) sequence, as well as the N terminus, are in good accordance with those determined for the ADH purified from M. bovis BCG extracts. The M. bovis BCG cloned adh gene was expressed in Escherichia coli by its own promoter and the synthesized product shows ADH activity in the butane-1-ol-NADP system. Based on comparison of the aa sequence, this enzyme belongs to the zinc-containing, long-chain alcohol/polyol dehydrogenase family, which has been primarily described in eukaryotes. Of the 22 strictly conserved residues in this group, 19 are also conserved in M. bovis BCG ADH (BCGADH).

Specific covalent fixation of chelating agents on peptides

The synthesis of two selectively protected bifunctional analogues of ethylenediaminetetra-acetic acid (EDTA) is described. In these analogues the four carboxy groups involved in chelation are protected as benzyl or t-butyl esters, while the fifth one, which is free, allows their coupling in a predetermined position to a nucleophilic group. An example of their use in solid phase peptide synthesis is given.

Formation of Nε-Dnp lysine during deprotection of Nε-Fmoc lysine in Nim-Dnp-histidine-containing peptides

Abstract The 2,4-dinitrophenyl group used for histidine side chain protection is not stable during aminolytic removal of Fmoc protecting groups. In the presence

Protection of Mice and Nude Rats Against Toxoplasmosis by an Octameric Construct of the P30 48–67 Peptide

The sequence of the first 20 NH2-terminus residues of P30 were obtained from this major surface antigen of T. gondii purified by HPLC. A synthetic peptide (P30 48–67) has been prepared both in linear form and as an octameric construction. Immunization of mice and rats with the P30 48–67 octamer in the presence of IFA induces high levels of IgG antibodies which recognize both the monomelic and the octameric peptides in ELISA, and P30 in Western blots of NP40-extracted tachyzoite antigens. Since these sera are negative in immunofluorescence assays with whole tachyzoites, it seems that IgG antibodies induced by P30 48–67 octamer, although recognizing the denatured structure, are unable to recognize the native protein. The protective effect of both constructs has been studied in mice and Nude rats. Whereas immunization of mice with the monomelic peptide does not confer any protection against oral infection with 1200 cysts of T. gondii 76K strain (mortality within 11 days), 40% of mice immunized with the octameric construct survived up to 75 days after infection. Nude rats were passively transferred with 5 x104 T lymphocytes from P30 48–67 octamer-immunized Fischer rats before infection with 5 x 104 RH strain tachyzoites. When compared to Nude rats transferred with control T lymphocytes, they presented an almost two-fold increase in their mean survival time and raised an intense IgG antibody response against P30. This shows that immunization with P30 48–67 MAP also induces an efficient T cell immune response.