Molecular characterization of a neutralizing murine monoclonal antibody against Tityus serrulatus scorpion venom

Monoclonal antibodies (mAbs) against Tityus serrulatus venom were obtained by the fusion of SP2/0 murine myeloma cells and spleen cells from BALB/c mice immunized with a toxic fraction (TstFG50) of the Tityus venom (this G50 chromatography fraction represents most of the toxicity of the crude venom) conjugated to bovine serum albumin (BSA) with glutaraldehyde. From the initial screening of over 200 hybridoma fusion wells, a panel of 9 anti-TstFG50 secreting hybridomas was established. The capacity of mAbs to neutralize the TstFG50 toxic fraction toxic was determined by in vitro neutralization assays and by inhibition of the binding of 125I-TsVII to its site on rat brain synaptosomes. Only mAbTs1 neutralized 50% of the toxic effects produced by scorpion venom and showed 35% inhibition of the binding of 125I-TsVII at 10(-7) M. To map the epitope recognized by the protective mAbTs1, we prepared a comprehensive series of overlapping 15-mer synthetic peptides covering the amino acid sequences of the four Tityus proteins. MAbTs1 reacted with peptide 26 of TsIV (KKSKDKKADSGYSYW), peptide 30 of TsVII (KKGSSGYSAWPASYS) and peptide 31 of TsNTxP (KKGSSGYSAWPASYS). MAbTs1 was not reactive with any peptide from TsII. The N-terminal lysine residue from the epitope was found to be critical for mAbTs1 binding. The epitope was positioned on the available three-dimensional structure of TsVII together with the recently identified residues from the pharmacophore of beta-scorpion toxins. The neutralizing properties of mAbTs1 might be explained by spatial vicinity of epitope residues with pharmacophore residues.

Localization of epitopes in the toxins of Tityus serrulatus scorpions and neutralizing potential of therapeutic antivenoms

Overlapping pentadecapeptides covering the complete amino acid sequence of TsII, TsVII and TsIV toxins from the venom of scorpion Tityus serrulatus (Ts), were prepared by use of the Spot method of multiple peptide synthesis. Horse anti-Ts antisera for therapeutic use were tested for their binding to peptides. All nine antisera tested showed reactivity with several peptides from the three toxins. Three antigenic regions, one in the very N-terminal, the second in the central part and the other in the C-terminal part of the three toxins were frequently, but not constantly recognized, with an intensity that seemed to be related to the neutralizing potency of the tested antivenom. Thus the corresponding peptides (residues 1-15 and 48-62 of TsII; residues 1-15, 16-30 and 48-62 of TsIV and residues 1-15 and 47-61 of TsVII) were synthesized, coupled to KLH and used as antigens to coat the microtitration plates to determine any relationship between their ELISA reactivity with therapeutic horse antivenoms and the neutralizing potential of these antivenoms. The mixture of the N-terminal peptide of TsII, of the N-terminal TsVII peptide and of the C-terminal of TsIV was found to give a linear relationship with the neutralizing titer of horse serum of low neutralizing potency (< or =1 mg/ml). However, high neutralizing antivenoms did not show the expected response in peptide ELISA. This observation is discussed in the context of the occurrence of continuous and discontinuous epitopes on toxins.

Identification of the mammalian Not gene via a phylogenomic approach

Despite the great morphological diversity of early embryos, the underlying mechanisms of gastrulation are known to be broadly conserved in vertebrates. However, a number of genes characterized as fulfilling an essential function in this process in several model organisms display no clear ortholog in mammalian genomes. We have devised an in silico phylogenomic approach, based on exhaustive similarity searches in vertebrate genomes and subsequent bayesian phylogenetic analyses, to identify such missing genes, presumed to be highly divergent. This approach has been used to identify mammalian orthologs of Not, an homeodomain containing gene previously characterized in Xenopus, chick and zebrafish as playing a critical role in the formation of the notochord. This attempt led to the identification of a highly divergent mammalian Not-related gene in the mouse, human and rat. The results from phylogenetic reconstructions, synteny analyses, expression pattern analyses in wild-type and mutant mouse embryos, and overexpression experiments in Xenopus embryos converge to confirm these genes as representatives of the Not family in mammals. The identification of the mammalian Not gene delivers an important component for the understanding of the genetics underlying notochord formation in mammals and its evolution among vertebrates. The phylogenomic method used to retrieve this gene thus provides a tool, which can complement or validate genome annotations in situations when they are weakly supported.

Epitope mapping of the antigenic protein TsNTxP from Tityus serrulatus scorpion venom using mouse, rabbit and sheep antibodies

In the present investigation we used native and recombinant TsNTxP to elicit antibodies in three different animal models (mouse, rabbit and sheep). Differences among anti-TsNTxP antibodies were analyzed using sets of overlapping pentadecapeptides of the TsNTxP amino acid sequence and also modified peptides to reveal key residues in antibody-peptide binding. Despite the identification of similar peptides by the antibodies in the C and N-terminal, peculiarities of each system were observed including the level of reactivity and also the number and type of key residues in the continuous epitopes of TsNTxP. In addition, in vitro neutralization assays indicated that sheep are an alternative and efficient model for the production of anti-Tityus serrulatus venom.

Molecular characterization of protective antibodies raised in mice by Tityus serrulatus scorpion venom toxins conjugated to bovine serum albumin

The possibility of raising a humoral immune response capable of inducing in vivo protection against the lethal effects of Tityus serrulatus (Ts) scorpion venom was evaluated in the mouse model. An immunogen was prepared that consists of a toxic fraction (TstFG(50)) of the Tityus venom (this G(50) chromatography fraction represents most of the toxicity of the crude venom) conjugated to bovine serum albumin (BSA) with glutaraldehyde. TstFG(50) coupled to BSA yielded a thoroughly detoxified immunogen. BALB/c and C57BL/10 mice were immunized with this preparation and all developed an antibody response. In vivo protection assays one week after the last immunization showed that vaccinated mice could resist the challenge by twice the LD(50) of the TstFG(50), a dose which killed all control non-immune mice. The protective effect persisted nine weeks after the end of the immunization protocol. To characterize epitopes of protective antibodies we used the Spot method of multiple peptide synthesis to prepare sets of immobilized 15 mer overlapping peptides, covering the complete amino acid sequences of the main Tityus toxins, TsII and TsVII (both beta-type toxins) and TsIV, an alpha-type toxin that is the major lethal component of the venom. Antibody binding to peptides, revealed one major antigenic region in the C-terminal part of the three toxins and another region in the helical part of TsII and TsIV toxins. It is likely that these epitopes correspond to neutralizing epitopes since they correspond to regions of the toxins that are known to be involved in the active site of the toxins.

Neutralizing antibodies to hepatitis C virus (HCV) in immune globulins derived from anti-HCV-positive plasma

The role of humoral immunity in hepatitis C virus (HCV) infections is uncertain. Nevertheless, there is increasing evidence for neutralizing antibodies to HCV in the serum or plasma of chronically infected individuals. Immune globulins prepared by ethanol fractionation of plasma had long been considered safe until a commercial immune globulin product, Gammagard, prepared from plasma from which units containing anti-HCV had been excluded, transmitted HCV to recipients. Studies suggested that the exclusion might have removed neutralizing antibodies from the plasma and hence compromised the safety of the resulting immune globulins. In the present study, by using chimpanzees and a recently validated in vitro system based on neutralization of infectious HCV pseudoparticles, we found broadly reactive neutralizing and protective antibodies in experimental immune globulin preparations made from anti-HCV-positive donations. Neutralizing antibodies were also found in Gammagard lots made from unscreened plasma that did not transmit hepatitis C but not in Gammagard lots, which were prepared from anti-HCV-screened plasma, that did transmit hepatitis C. The results provide an explanation for the mechanism by which the safety of this product was compromised. Immune globulins made from anti-HCV-positive plasma and containing broadly reactive neutralizing antibodies may provide a method of preventing HCV infection.

In vitro assay for neutralizing antibody to hepatitis C virus: evidence for broadly conserved neutralization epitopes

Our understanding of the humoral immune response to hepatitis C virus (HCV) is limited because the virus can be studied only in humans and chimpanzees and because previously described neutralization assays have not been robust or simple to perform. Nevertheless, epidemiologic and laboratory studies suggested that neutralizing Ab to HCV might be important in preventing infection. We have recently described a neutralization assay based on the neutralization of pseudotyped murine retrovirus constructs bearing HCV envelope glycoproteins on their surface. We have applied the assay to well characterized clinical samples from HCV-infected patients and chimpanzees, confirmed the existence of neutralizing Ab to HCV, and validated most previously reported neutralizations of the virus. We did not find neutralizing anti-HCV in resolving infections but did find relatively high titers (>1:320) of such Ab in chronic infections. Neutralizing Ab was directed not only to epitope(s) in the hypervariable region of the E2 envelope protein but also to one or more epitopes elsewhere in the envelope of the virus. Neutralizing Ab was broadly reactive and could neutralize pseudotype particles bearing the envelope glycoproteins of two different subgenotypes (1a and 1b). The ability to assay neutralizing anti-HCV should permit an assessment of the prospects for successful Ab-mediated passive and active immunoprophylaxis against hepatitis C.

Cell entry of hepatitis C virus requires a set of co-receptors that include the CD81 tetraspanin and the SR-B1 scavenger receptor

Several cell surface molecules have been proposed as receptor candidates, mediating cell entry of hepatitis C virus (HCV) on the basis of their physical association with virions or with soluble HCV E2 glycoproteins. However, due to the lack of infectious HCV particles, evidence that these receptor candidates support infection was missing. Using our recently described infectious HCV pseudotype particles (HCVpp) that display functional E1E2 glycoprotein complexes, here we show that HCV is a pH-dependent virus, implying that its receptor component(s) mediate virion internalization by endocytosis. Expression of the CD81 tetraspanin in non-permissive CD81-negative hepato-carcinoma cells was sufficient to restore susceptibility to HCVpp infection, confirming its critical role as a cell attachment factor. As a cell surface molecule likely to mediate endosomal trafficking, we demonstrate that the human scavenger receptor class B type 1 (SR-B1), a high-density lipoprotein-internalization molecule that we previously proposed as a novel HCV receptor candidate due to its affinity with E2 glycoproteins, is required for infection of CD81-expressing hepatic cells. By receptor competition assays, we found that SR-B1 antibodies that blocked binding of soluble E2 could prevent HCVpp infectivity. Furthermore, we establish that the hyper-variable region 1 of the HCV E2 glycoprotein is a critical determinant mediating entry in SR-B1-positive cells. Finally, by correlating expression of HCV receptors and infectivity, we suggest that, besides CD81 and SR-B1, additional hepatocyte-specific co-factor(s) are necessary for HCV entry.

In vitro effect of essential oils from Cinnamomum aromaticum, Citrus limon and Allium sativum on two intestinal flagellates of poultry, Tetratrichomonas gallinarum and Histomonas meleagridis

Essential oils may be effective preventive or curative treatments against several flagelated poultry parasites and may become primordial either to organic farms, or as more drugs are bannished. The anti-flagellate activity of essential oils obtained from fresh leaves of Cinnamomum aromaticum, Citrus limon pericarps and Allium sativum bulbs was investigated in vitro on Tetratrichomonas gallinarum and Histomonas meleagridis. On T. gallinarum, the minimal lethal concentration (MLC) at 24 hours was 0.25 microliter/ml for C. aromaticum oil, and 0.125 microliter/ml for C. limon and A. sativum oils. On H. meleagridis, MLC was 0.5 microliter/ml for C. aromaticum oil and 1 microliter/ml for C. limon and A. sativum oils at 24 and 48 hours. Moreover, no synergistic effects were evidenced in vitro. The essential oil constituents, based on their GC retention times have been also identified. The major component is trans-cinnamaldehyde (79%) for C. aromaticum; limonene for C. limon (71%) and diallyl tri- and disulfide (79%) for A. sativum. Even if concentration and protocol adaptations are required for successful in vivo treatments, it appears that these oils may be useful as chemotherapeutic agents against several poultry parasites.

Evaluation of cardiac troponin I and T levels as markers of myocardial damage in doxorubicin-induced cardiomyopathy rats, and their relationship with echocardiographic and histological findings

BACKGROUND

Cardiac troponins I (cTnI) and T (cTnT) have been shown to be highly sensitive and specific markers of myocardial cell injury. We investigated the diagnostic value of cTnI and cTnT for the diagnosis of myocardial damage in a rat model of doxorubicin (DOX)-induced cardiomyopathy, and we examined the relationship between serial cTnI and cTnT with the development of cardiac disorders monitored by echocardiography and histological examinations in this model.

METHODS

Thirty-five Wistar rats were given 1.5 mg/kg DOX, i.v., weekly for up to 8 weeks for a total cumulative dose of 12 mg/kg BW. Ten rats received saline as a control group. cTnI was measured with Access(R) (ng/ml) and a research immunoassay (pg/ml), and compared with cTnT, CK-MB mass and CK. By using transthoracic echocardiography, anterior and posterior wall thickness, LV diameters and LV fractional shortening (FS) were measured in all rats before DOX or saline, and at weeks 6 and 9 after treatment in all surviving rats. Histology was performed in DOX-rats at 6 and 9 weeks after the last DOX dose and in all controls.

RESULTS

Eighteen of the DOX rats died prematurely of general toxicity during the 9-week period. End-diastolic (ED) and end-systolic (ES) LV diameters/BW significantly increased, whereas LV FS was decreased after 9 weeks in the DOX group (p<0.001). These parameters remained unchanged in controls. Histological evaluation of hearts from all rats given DOX revealed significant slight degrees of perivascular and interstitial fibrosis. In 7 of the 18 rats, degeneration and myocyte vacuolisation were found. Only five of the controls exhibited evidence of very slight perivascular fibrosis. A significant rise in cTnT was found in DOX rats after cumulative doses of 7.5 and 12 mg/kg in comparison with baseline (p<0.05). cTnT found in rats after 12 mg/kg were significantly greater than that found after 7.5 mg/kg DOX. Maximal cTnI (pg/ml) and cTnT levels were significantly increased in DOX rats compared with controls (p=0.006, 0.007). cTnI (ng/ml), CK-MB mass and CK remained unchanged in DOX rats compared with controls. All markers remained stable in controls. Analysis of data revealed a significant correlation between maximal cTnT and ED and ES LV diameters/BW (r=0.81 and 0.65; p<0.0001). A significant relationship was observed between maximal cTnT and the extent of myocardial morphological changes, and between LV diameters/BW and histological findings.

CONCLUSIONS

Among markers of ischemic injury after DOX in rats, cTnT showed the greatest ability to detect myocardial damage assessed by echocardiographic detection and histological changes. Although there was a discrepancy between the amount of cTnI and cTnT after DOX, probably due to heterogeneity in cross-reactivities of mAbs to various cTnI and cTnT forms, it is likely that cTnT in rats after DOX indicates cell damage determined by the magnitude of injury induced and that cTnT should be a useful marker for the prediction of experimentally induced cardiotoxicity and possibly for cardioprotective experiments.

Null mutation of DNA strand break-binding molecule poly(ADP-ribose) polymerase causes medulloblastomas in p53(-/-) mice

Medulloblastoma is an invasive embryonal tumor of the cerebellum with predominant neuronal differentiation. Although several genes have been implicated in medulloblasoma formation, such as Patched (Ptc1) and the adenomatous polyposis coli gene (Apc), the majority of these tumors cannot be explained by mutations in these genes. The cellular origin as well as the genetic and molecular changes involved in the genesis and progression of human medulloblastomas remain largely unknown. Here we show that disruption of poly(ADP-ribose) polymerase (PARP-1) causes a high incidence (49%) of aggressive brain tumors in p53 null mice, with typical features of human cerebellar medulloblastomas. At as early as 8 weeks of age, lesions started on the outer surface of the cerebellum from remnant granule cell precursors of the developmental external germinal layer. Progression of these tumors is associated with the re-activation of the neuronal specific transcription factor Math1, dysregulation of Shh/Ptc1 signaling pathway, and chromosomal aberrations, including triradial and quadriradial chromosomes. The present study indicates that the loss of function of DNA double-strand break-sensing and repair molecules is an etiological factor in the evolution of the cerebellar medulloblastomas. These PARP-1/p53 double null mice represent a novel model for the pathogenesis of human medulloblastomas.

In vitro activity of therapeutic drugs against Histomonas meleagridis (Smith, 1895)

Histomoniasis or blackhead is a life-threatening disease of turkeys that is caused by a flagellated protozoan, Histomonas meleagridis. The development of an assay to measure the sensitivity of drugs traditionally used against this parasite, as reputed to be effective against other protozoan parasites, is described. The in vitro minimum lethal concentrations (MLC), time for drug efficacy, and parasite viability after removal of residual drugs were determined. Three of the 10 tested drugs, fenbendazole, albendazole, and sulfadiazine, were found to be ineffective against H. meleagridis. Nifursol, the only compound still authorized as a feed additive in Europe, is an inhibiting agent but is not lethal in vitro. Roxarsone, an arsenical derivate similar to nitarsone (the only authorized drug in United States), is effective at high concentration (200 microg/mL) after a long exposure (48 h). The lethal activity of dimetridazole, metronidazole, ronidazole, tinidazole, and furazolidone in vitro was demonstrated. Dimetridazole (MLC = 25 microg/mL after 6 h of exposure), metronidazole (MLC = 50 microg/mL after 24 h), and furazolidone (MLC = 50 microg/mL after 24 h) are rapidly effective at low concentrations. These results confirm the effectiveness of dimetridazole, a drug that has been used in the treatment and prevention of blackhead. In May 2002 this compound was removed as feed additive in Europe.

The chimeric mouse-human anti-CD4 Fab 13B8.2 expressed in baculovirus inhibits both antigen presentation and HIV-1 promoter activation

The anti-CD4 mAb 13B8.2, directed against the CDR3-like loop of the D1 domain of CD4, inhibits signal transduction pathways leading to both T cell activation and HIV replication. VH9/DSP2/JH2 and Vkappa12-13/Jkappa2 rearrangements, corresponding to genes encoding the heavy and light chain variable regions of the 13B8.2 mAb, were inserted into baculovirus cassettes upstream from pre-installed human Fdgamma1 and Ckappa genes, respectively. After expression in insect cells, a complete correctly-processed Fab was secreted into the culture medium; it was protein-G immunopurified with a yield of 5 mg/L. The chimeric Fab 13B8.2 showed anti-CD4 binding activity with an affinity value of 3.3 nM and recognized the same region on the CDR3-like loop as the parental mAb. The mouse-human Fab inhibited IL2 secretion following antigen presentation and displayed a strong capacity to prevent HIV-1 promoter activation. Taken together, these results indicate that the chimeric Fab retained a major part of the parental 13B8.2 mAb properties and suggest that it might be a valuable therapeutic tool.

Induction of neutralizing antibodies against Tityus serrulatus scorpion toxins by immunization with a mixture of defined synthetic epitopes

We have used the Spot method of multiple peptide synthesis to prepare sets of immobilized overlapping peptides of uniform size (15 mer), covering the complete amino acid sequences of TsNTxP a non-toxic and immunogenic protein and TsIV, an alpha-type toxin that is the major lethal component of the venom of scorpion Tityus serrulatus. Anti-TsNTxP antibodies binding to peptides, revealed three antigenic regions, one in the N-terminal, the second in the central part and the other in the C-terminal part of TsNTxP. One peptide epitope in the C-terminal part of TsIV was identified with anti-TsIV neutralizing rabbit antibodies. Anti-peptide antibodies were raised against these four peptides all together covalently coupled to keyhole limpet hemocyanin (KLH) and found to neutralize in vitro the toxic effects of the T. serrulatus venom. Quantities of venom equivalent to 13.5 LD(50) were effectively neutralized by 1ml of the anti-peptide serum. The antigenic specificities of the anti-peptides were compared by an indirect enzyme-linked immunosorbent assay (ELISA) using synthetic peptides and crude venoms from T. serrulatus, T. bahiensis, T. cambridgei, T. stigmurus, Androctonus autralis Hector and Centruroides sculpturatus to coat the microtitration plates. The anti-peptide antibodies had a comparable high reactivity with the crude venom of T. serrulatus, moderate binding to T. bahiensis, T. cambridgei, T. stigmurus and Centruroides sculpturatus venoms but were unable to recognize the venom of Androctonus autralis Hector. These results show that by using peptides derived from the sequence of scorpion toxins, the generation of anti-peptide antibodies able to neutralize the cognate venom appears to be an alternative strategy for the easy preparation of antivenoms.

Efficient CD4 binding and immunosuppressive properties of the 13B8.2 monoclonal antibody are displayed by its CDR-H1-derived peptide CB1

A systematic exploration of the V(H)2/V(kappa)12-13 variable domains of the anti-CD4 monoclonal antibody (mAb) 13B8.2 was performed by the Spot method to screen for paratope-derived peptides (PDPs) demonstrating CD4 binding ability. Nine peptides, named CB1 to CB9, were identified, synthesized in a cyclic and soluble form and tested for binding to recombinant soluble CD4. Among them, CB1, CB2 and CB8 showed high anti-CD4 activity. Competition studies for CD4 binding indicated that PDPs CB1, CB8, and the parental mAb 13B8.2 recognized the same complementarity determining region (CDR)3-like loop region. PDP CB1 was shown to mimic the biological properties of 13B8.2 mAb in two independent cellular assays, demonstrating inhibitory activities in the micromolar range on antigen presentation and human immunodeficiency virus promoter activation. Our results indicate that the bioactive CDR-H1 PDP CB1 has retained a significant part of the parental 13B8.2 mAb properties and might be a lead for the design of anti-CD4 peptidomimetics of clinical interest.

Interaction of the octapeptide angiotensin II with a high-affinity single-chain Fv and with peptides derived from the antibody paratope

The amino-acid sequence of the very high-affinity anti-angiotensin II monoclonal antibody 4D8 was predicted from the nucleotide sequence of the heavy and light chain variable genes. The single-chain variable fragment (scFv) was constructed and expressed in Escherichia coli as a soluble protein and at the surface of the filamentous M13 phage and was compared with the full-length antibody (Ab). The scFv showed the same specificity profile and affinity constant as the intact antibody (5.0x10(10) and 8.0x10(10) M(-1), respectively, by Scatchard analysis). Several peptides from the set of overlapping dodecapeptides covering the variable domains of 4D8 mAb were found to specifically bind biotinylated angiotensin II: peptides from the L1, L2, L3 and H1 regions had the strongest capacity to bind the antigen.

Analysis of cell division parameters and cell cycle gene expression during the cultivation of Arabidopsis thaliana cell suspensions

Arabidopsis thaliana cell suspension cultures were characterized for the first time in detail in terms of biomass accumulation, cell division rate and cell cycle phase durations. Subsequently, this model system was used to follow the transcription profile of key cell cycle genes during a complete cultivation cycle. According to the calculated changes in the relative division rate over time, the cell cycle genes could be classified into four groups based on their transcriptional expression pattern. These differential patterns of gene expression are discussed with respect to the putative roles of the different cell cycle genes in the division cycle. Analysis of protein levels showed that mRNA levels did not correlate with protein levels in all cases. Results obtained in other systems, such as BY-2 cell suspensions or plants, confirm that cell suspension cultures of A. thaliana are suitable for the analysis of cell cycle regulation.

Carcinoembryonic antigen continuous epitopes determined by the spot method

Carcinoembryonic antigen (CEA) is a heavily glycosylated tumor-associated protein with an N-A1-B1-A2-B2-A3-B3 domain structure. Circulating CEA immunoassays are used for monitoring digestive cancer patients, and radiolabeled anti-CEA monoclonal antibodies (MAb) are used for the diagnosis and therapy of CEA-positive tumors. The five major nonoverlapping epitopes (Gold 1-5) have been broadly correlated with the domain organization, but there is no precise localization of the epitopes at the sequence level. In an attempt to identify the peptide sequences corresponding to the five Gold epitopes on the CEA molecule, we prepared a set of 227 overlapping fifteen-mer peptides corresponding to the complete CEA sequence with the SPOT method. Using five high affinity MAbs directed against the five CEA Gold epitopes, we demonstrated that none of these epitopes could be mimicked by a fifteen-mer peptide sequence. However, using rabbit and goat anti-CEA sera, we identified six major continuous antigenic regions. All are included in the Ig-like domains of the CEA: two in the A1 domain (residues 120-134 and 153-164), one each in the A2 (329-337) and A3 domains (508-513), one at the junction between the A3 and B3 domains (553-561) and one in the B3 domain (565-573). A very homologous sequence (common residues VSPRL) was mapped in each of the three A domains. Thus, in terms of occurrence of continuous epitopes, the Ig-like domains A1, A2, A3 and B3 seem to be the most antigenic parts of CEA. These peptide sequences should be good candidates for the future development of site-specific anti-CEA MAbs.

Delineation of a linear epitope by multiple peptide synthesis and phage display

Two different approaches, the phage display technique and the Spot peptide synthesis on cellulose membranes, were used to identify sequences recognized by Fab 57P, specific for tobacco mosaic virus protein (TMVP), and define the preferred chemical composition of a functional epitope. Kinetic measurements of the interaction between peptide variants and the antibody fragment were used to further refine the molecular basis of binding activity. Our results show that the functional epitope of Fab 57P requires precise physico-chemical properties at a limited number of positions, and that residues flanking these key residues can influence binding affinity. The phage display and Spot synthesis methods allowed the straightforward localization of the binding region and the identification of residues that are essential for recognition. However, these methods yielded slightly different views of accessory factors that are able to influence antibody binding. The influence on binding activity of these factors can only be assessed through quantitative affinity measurements.

Spatial distribution of cell division rate can be deduced from that of p34(cdc2) kinase activity in maize leaves grown at contrasting temperatures and soil water conditions

We have investigated the spatial distributions of cell division rate, p34(cdc2) kinase activity, and amount of p34(cdc2a) in maize (Zea mays) leaves grown at contrasting temperatures and soil water conditions. An original method for calculating cell division rate in all leaf tissues is proposed. In all studied conditions, cell division rate was stable and maximum in the first 2 cm beyond the leaf insertion point, declined afterward, and reached zero at 7 cm from the insertion point. The spatial distribution of p34(cdc2) kinase activity, expressed on a per cell basis, followed the same pattern. In contrast, the amount of p34(cdc2a) was maximum in the first centimeter of the leaf, declined afterward, but remained at 20% of maximum in more distal zones with a near-zero cell division rate. A mild water deficit caused a reduction in cell division rate and p34(cdc2) kinase activity by approximately 45% in all leaf zones, but did not affect the amount of p34(cdc2a). Growth temperature affected to the same extent cell division rate and p34(cdc2) kinase activity, but only if p34(cdc2) kinase activity was assayed at growth temperature, and not if a standard temperature was used in all assays. A common linear relationship between cell division rate and p34(cdc2) kinase activity applied to all causes of changes in cell division rate, i.e. cell aging, water deficit, or changes in temperature. It is shown that temperature has two distinct and additive effects on p34(cdc2) kinase activity; first, an effect on the rate of the reaction, and second, an effect on the amount of p34(cdc2a).

Critical residues of epitopes recognized by several anti-p53 monoclonal antibodies correspond to key residues of p53 involved in interactions with the mdm2 protein

The aim of this work was to study the reactivity of antibodies directed against the N-terminus of p53 protein. First, we analysed the cross-reactivity of anti-p53 antibodies from human, mouse and rabbit sera with peptides derived from human, mouse and Xenopus p53. Next, we characterized more precisely a series of monoclonal antibodies directed against the N-terminal part of p53 and produced by immunizing mice with either full length human or Xenopus p53. For each of these mAbs we localized the epitope recognized on human p53 by the Spot method of multiple peptide synthesis, defined critical residues on p53 involved in the interaction by alanine scanning replacement experiments and determined kinetic parameters using real-time interaction analysis. These antibodies could be divided into two groups according to their epitopic and kinetic characteristics and their cross-reactivity with murine p53. Our results indicate that critical residues involved in the interaction of some of these mAbs with p53 correspond to key residues on p53 involved in its interaction with the mdm2 protein. These antibodies could, therefore, represent powerful tools for the study of p53 regulation.

Spatial distributions of expansion rate, cell division rate and cell size in maize leaves: a synthesis of the effects of soil water status, evaporative demand and temperature

The spatial distributions of leaf expansion rate, cell division rate and cell size was examined under contrasting soil water conditions, evaporative demands and temperatures in a series of experiments carried out in either constant or naturally fluctuating conditions. They were examined in the epidermis and all leaf tissues. (1) Meristem temperature affected relative elongation rate by a constant ratio at all positions in the leaf. If expressed per unit thermal time, the distribution of relative expansion rate was independent of temperature and was similar in all experiments with low evaporative demand and no water deficit. This provides a reference distribution, characteristic of the studied genotype, to which any distribution in stressed plants can be compared. (2) Evaporative demand and soil water deficit affected independently the distribution of relative elongation rate and had near-additive effects. For a given stress, a nearly constant difference was observed, at all positions of the leaf, between the relative elongation rates of stressed plants and those of control plants. This caused a reduction in the length of the zone with tissue elongation. (3) Methods for calculating cell division rate in the epidermis and in all leaf tissues are proposed and discussed. In control plants, the zone with cell division was 30 mm and 60 mm long in the epidermis and in whole tissues, respectively. Both this length and relative division rate were reduced by soil water deficit. The size of epidermal and of mesophyll cells was nearly unaffected in the leaf zone with both cell division and tissue expansion, suggesting that water deficit affects tissue expansion rate and cell division rate to the same extent. Conversely, cell size of epidermis and mesophyll were reduced by water deficit in mature parts of the leaf.

Systematic mapping of regions of human cardiac troponin I involved in binding to cardiac troponin C: N- and C-terminal low affinity contributing regions

The Spot method of multiple peptide synthesis was used to map in a systematic manner regions of the human cardiac troponin I sequence (hcTnI) involved in interactions with its physiological partner, troponin C (cTnC). Ninety-six 20-mer peptides describing the entire hcTnI sequence were chemically assembled; their reactivity with [125I]cTnC, in the presence of 3 mM Ca2+, enabled the assignment of six sites of interaction (residues 19-32, 45-54, 129-138, 145-164, 161-178 and 191-210). For several sites, a good correlation with literature data was obtained, thus validating this methodological approach. Synthetic peptides, each containing in their sequence an interaction site, were prepared. As assessed by BIACORE, all of them exhibited an affinity for cTnC in the range of 10(-6)-10(-7) M, except for hcTnI [39-58] which showed a nanomolar affinity. This peptide was also able to block the interaction between hcTnI and cTnC. We therefore postulate that despite the existence of multiple cTnC interaction sites on the hcTnI molecule, only that region of hcTnI allows a stabilization of the complex. Residues 19-32 from the N-terminal cardio-specific extension of hcTnI were also found to be involved in interaction with cTnC; residues 19-32 may correspond to the minimal sequence of the extension which could switch between the N- and C-terminal TnC domains, depending on its phosphorylation state. Finally, two Ca(2+)-dependent cTnC binding domains within the C-terminal part of hcTnI (residues 164-178 and 191-210) were also mapped. The latter site may be linked with the cardiac dysfunction observed in stunned myocardium.