PubMed Health⌕ Search

Biomedical subjects

D G Russell

Publications and source records attributed to D G Russell.

At least 109 records · Page 6Linked to original sources
PubMed1989

The promastigote surface protease (gp63) of Leishmania is expressed but differentially processed and localized in the amastigote stage.

The expression, processing and localization of the promastigote surface glycoprotein, gp63, in the amastigote form of Leishmania mexicana was examined. Metabolically labeled protein was immunoprecipitated from promastigotes and amastigotes. The isolated proteins were subjected to deglycosylation and partial peptide mapping. The cleavage products generated migrated similarly in sodium dodecyl sulfate-polyacrylamide gel electrophoresis, indicating that the proteins were closely related. The majority of gp63 in amastigotes was inaccessible to surface-labeling procedures, and lacked the phosphatidylinositol membrane anchor. Immunolocalization of this subpopulation of gp63 revealed it to be present within the parasite's flagellar pocket. Despite the relative paucity of 'membrane-form' gp63, isolation and analysis of surface proteins from lesion amastigotes indicated that gp63 was the most abundant protein on the amastigote surface.

Animals↗
PubMed1989

Leishmania and the macrophage: a marriage of inconvenience.

The Leishmania protozoan successfully parasitizes the macrophage of its vertebrate host. Considerable interest now centres on the identification of the parasite ligands and the macrophage receptors to which they bind. In this article, David Russell and Patricia Talamas-Rohana discuss the attachment mechanisms of Leishmania promastigotes to macrophages, and the possible role of complement components in their opsonization.

Animals↗
PubMed1989

Antibodies raised against synthetic peptides from the Arg-Gly-Asp-containing region of the Leishmania surface protein gp63 cross-react with human C3 and interfere with gp63-mediated binding to macrophages.

The Leishmania surface glycoprotein gp63 binds to complement receptor type 3 on the macrophage surface. Antibody raised against a synthetic peptide containing the Arg-Gly-Asp region of the amino acid sequence of gp63 recognizes both gp63 and the alpha-chain of human C3. Monovalent Fab fragments from this antibody block gp63-mediated binding to macrophages.

Amino Acid Sequence↗
PubMed1988

Complement receptor type 3 (CR3) binds to an Arg-Gly-Asp-containing region of the major surface glycoprotein, gp63, of Leishmania promastigotes.

The major surface glycoprotein of Leishmania promastigotes, gp63, was isolated and reconstituted into a lipid membrane immobilized on the surface of 5-micron-diameter silica beads. These beads bound to the macrophage (MO), and the extent of binding correlated with the density of gp63 on the bead. The bead thus facilitated analysis of the binding specificity of a single ligand, gp63, without contribution from other molecules present on the surface of intact promastigotes. Plating of MO onto substrates coated with antibodies directed against several cell surface receptors indicated that the complement receptor CR3 was necessary for binding gp63. CR3 recognizes a portion of C3 that contains the sequence R G D. Since gp63 also contains such a sequence, we tested the ability of a synthetic peptide based on the R G D-containing region of gp63 to inhibit the binding of gp63 beads. The R G D-containing peptide from gp63 inhibited the binding of both gp63 beads and EC3bi to MO. Similarly, peptides previously shown to inhibit the binding of C3bi also inhibited the attachment of gp63 beads. The synthetic peptide from the R G D region of gp63 also reduced the binding of intact promastigotes to MO. These results indicate that gp63 binds directly to CR3.

Amino Acid Sequence↗
PubMed1988

Effective immunization against cutaneous leishmaniasis with defined membrane antigens reconstituted into liposomes.

The abundant Leishmania promastigote surface Ag gp63 and Leishmania promastigote lipophosphoglycan were reconstituted into liposomes and used as a vaccine against the agent of New World cutaneous leishmaniasis, Leishmania mexicana. The Ag were inoculated s.c., i.p., and i.v. into CBA/ca and BALB/c mice. Even at low Ag dosages, 8 to 10 micrograms/mouse, the Ag induced appreciable levels of protection. In CBA/ca mice complete protection was obtained by s.c. inoculation of antigen-containing liposomes. Protection could be transferred with T cells to naive mice. Interestingly, the Ag-containing liposomes did not cause the disease exacerbation observed in previous vaccine studies with crude parasite extracts.

Animals↗
PubMed1987

The macrophage-attachment glycoprotein gp63 is the predominant C3-acceptor site on Leishmania mexicana promastigotes.

The interaction between Leishmania promastigotes and their vertebrate host's complement system results not only in parasite lysis but also, due to surface-bound complement components, in increased macrophage binding potential. In this study we demonstrate, with the use of isolated complement components, that activation is via the alternative complement pathway, initiated by direct deposition of C3 onto the parasite surface. The predominant C3 acceptor site on the promastigotes was initially identified as the glycoprotein gp63 by anti-C3 antibody immunoprecipitation of radioiodinated promastigotes following incubation in the alternative pathway initiators C3, and factors B and D. The C3-binding properties of gp63 were confirmed and quantified, in relation to other surface antigens, by incubating parasites in iodinated C3 and immunoprecipitating bound C3 with antibodies directed against different promastigote surface antigens. The other abundant surface antigen, the glycolipid 'excreted factor', did not show any C3-binding activity. Further demonstration was provided by incubating liposomes containing either gp63 or excreted factor in iodinated C3 and factors B and D. Only gp63-containing liposomes bound C3. Considering that both gp63 and the excreted factor have recently been implicated in attachment and uptake by macrophage, these findings may have considerable bearing in the determination of which of the macrophage surface receptors identify which parasite ligand.

Animals↗
PubMed1987

Subpellicular and flagellar microtubules of Trypanosoma brucei brucei contain the same alpha-tubulin isoforms.

The cytoskeleton of the parasitic hemoflagellate Trypanosoma brucei brucei essentially consists of two microtubule-based structures: a subpellicular layer of singlet microtubules, which are in close contact with the cell membrane, and the flagellar axoneme. In addition, the cells contain a small pool of soluble tubulin. Two-dimensional gel electrophoretic analysis of the tubulins present in these subcellular compartments revealed two distinct electrophoretic isoforms of alpha-tubulin, termed alpha 1 and alpha 3. alpha 1-Tubulin most likely represents the primary translation product, while alpha 3-tubulin is a posttranslationally acetylated derivative of alpha 1-tubulin. In the pool of soluble cytoplasmic tubulin, alpha 1 is the predominant species, while the very stable flagellar microtubules contain almost exclusively the alpha 3-tubulin isoform. The subpellicular microtubules contain both isoforms. Neither of the two alpha-tubulin isoforms is organelle specific, but the alpha 3 isoform is predominantly located in stable microtubules.

Acetates↗
PubMed1987

Characterization of Pales spermatocyte spindles, with reference to an MTOC-associated protein.

Pales ferruginea spermatocytes, because of their high proportion of dividing cells, offer many advantages in the study of the meiotic spindle. In the present study we have combined ultrastructural and immunofluorescence techniques with biochemical analysis of constituent spindle components. Using a centrosome-reactive serum, which recognizes an antigen in the centrosomal and midbody regions of dividing cells, we have identified an MTOC-associated polypeptide of 112,000 Mr with a pI of 5.6. The relative abundance of this protein in cells and isolated cytoskeletons indicates that it is present in other regions of the cell and is either more abundant, or is only recognized by the antibody in association with MTOCs.

Animals↗
PubMed1986

The involvement of the major surface glycoprotein (gp63) of Leishmania promastigotes in attachment to macrophages.

The interaction between the macrophage and the parasite plays a central role in the continued success of Leishmania infection. The promastigote surface ligand, and its complementary macrophage membrane receptor, involved in attachment and phagocytosis are likely to exert considerable influence over the outcome of a new infection. In this study, we report experiments pertaining to one such parasite membrane protein. Initial examination of promastigote surface proteins by radiolabeling and two-dimensional-polyacrylamide gel electrophoresis revealed an abundant polypeptide with an apparent m.w. of 63,000. Lectin-binding studies indicated that it was a glycoprotein containing mannose, N-acetyl glucosamine, and N-acetyl galactosamine residues. Monospecific antiserum raised against this glycoprotein, gp63, decorated the entire promastigote plasmalemma. Univalent antibody fragments from this antiserum blocked the interaction between promastigotes and macrophages by inhibiting attachment. Anti-gp63-inhibition reduced parasite/macrophage binding to 30 to 35% of the control binding level. Additional evidence of the involvement of gp63 in attachment to macrophages was provided by studies that made use of gp63-containing proteoliposomes. These vesicles were avidly phagocytosed by macrophages. Uptake of the gp63-containing liposomes was suppressed by greater than 90% by both anti-gp63 F(ab) fragments and the oligosaccharide mannan, indicating that their phagocytosis was receptor dependent. These results demonstrate that the abundant glycoprotein gp63 plays an important role in attachment of promastigotes to macrophages, and attachment via this parasite ligand is sufficient to trigger phagocytosis.

Adhesiveness↗
PubMed1986

Microtubular cytoskeletons of parasitic protozoa.

Shape, motility and division of eukaryotic cells are all determined to some extent by intracellular microtubules. Parasites, particularly protozoan parasites, offer important models for the study of microtubule organization, which may also provide useful leads for novel chemotherapeutic agents against parasite-specific forms of these organelles. Research on the biology of microtubules has advanced rapidly in the last 2-3 years, from purely descriptive studies to on understanding of some of the genetic and biochemical aspects. In this article, David Russell and Jean-François Dubremetz summarize the progress and discuss the potential of tubulin as a drug target for antiprotozool chemotherapy.

Journal Article↗
PubMed1984

Tubulin heterogeneity in the trypanosome Crithidia fasciculata.

The interphase cell of Crithidia fasciculata has three discrete tubulin populations: the subpellicular microtubules, the axonemal microtubules, and the nonpolymerized cytoplasmic pool protein. These three tubulin populations were independently and selectively purified, yielding, in each case, microtubule protein capable of self-assembly. All three preparations polymerized to form ribbons and sheets rather than the more usual microtubular structures. Analyses of the tubulin by two-dimensional polyacrylamide gel electrophoresis, isoelectric focusing, and peptide mapping indicated that the beta-tubulin complex remained constant regardless of source but that some heterogeneity was present in the alpha subunit. Cytoplasmic pool alpha tubulins (alpha 1/alpha 2) were the only alpha isotypes in the cytoplasm and also formed most of the alpha tubulin species in the pellicular fraction. Flagellar alpha tubulin (alpha 3) was the sole alpha isotype in the flagella; it appeared in small amounts in the pellicular fraction but was completely absent from the cytoplasm. In vitro translation products from polyadenylated RNA from C. fasciculata were also examined by two-dimensional polyacrylamide gel electrophoresis and possessed a protein corresponding to alpha 1/alpha 2 tubulin but lacked any alpha 3 tubulin. The alpha 3 polypeptide arose from a post-translational modification of a precursor polypeptide not identifiable by two-dimensional polyacrylamide gel electrophoresis as alpha 3. Peptide mapping data indicated that cytoplasmic alpha tubulin is the most likely precursor. These results demonstrate alpha-tubulin heterogeneity in this organism and also how close the relationship between flagellar and cytoskeletal tubulins can be among lower eucaryotes.

Animals↗
PubMed1984

Flagellar regeneration of the trypanosome Crithidia fasciculata involves post-translational modification of cytoplasmic alpha tubulin.

Deflagellation of Crithidia fasciculata stimulated formation of new flagella and maximized production of alpha 3 tubulin. Continuous labeling during reflagellation revealed that alpha 1, 2, and 3 tubulins were formed, whereas the polyadenylated RNA translation products lacked alpha 3 isoform. Pulse-chase labeling experiments demonstrated that alpha 3 was a post-translational modification of cytoplasmic alpha tubulin.

Animals↗
PubMed1984

The polar ring of coccidian sporozoites: a unique microtubule-organizing centre.

The infective stages, or 'zoites, of coccidian parasites possess an organized network of spirally arranged microtubules that closely follow the helical body shape of these vermiform cells. These subpellicular microtubules are anchored anteriorly by insertion into a highly structured circular microtubule-organizing centre (MTOC) known as the polar ring. This MTOC has been examined both in situ and in isolated, critical-point-dried whole cytoskeletons. The 24 microtubules attach laterally to the MTOC through shallow depressions on the inner face of the ring: the ends do not appear to be physically capped. The polar ring has no obvious or regular substructure, although it has a faintly fibrous appearance. The polarity of the microtubules, determined by 'hook decoration', is such that the plus or fast-growing end is distal to the MTOC. The coccidian 'zoite MTOC is unique both in its highly defined structure and in the degree of organization it confers upon the developing cell in terms of the number, spacing, orientation and polarity of the subpellicular microtubules.

Animals↗
PubMed1983

Host cell invasion by Apicomplexa: an expression of the parasite's contractile system?

Recent studies on the motility of coccidian sporozoites have demonstrated a membrane-associated contractile system capable of moving certain intramembraneous components down the parasite surface propelling it forwards. The properties of this system resemble recorded observations on host cell invasion. In this study the invasive behaviour of Eimeria tenella and E. acervulina has been examined, with reference to the above findings, by light microscope and scanning and transmission electron microscopes. Known inhibitors of motility prevent invasion, though attachment appears unaffected. Invasion itself consists of 3 phases; attachment and orientation, induction of a parasitophorous vacuole and translocation of the parasite into the vacuole. Ultrastructural examination reveals a close membrane/membrane association maintained throughout invasion. From these results it is suggested that the parasite enters the parasitophorous vacuole by 'capping' the host/parasite junction down its body, so locomoting into the host cell. Such a model has two main advantages; it requires no additional modifications to either cell, and the specificity of membrane receptors would enable the one membrane-associated contractile system to be responsible for locomotion, antibody capping and host cell invasion.

Adhesiveness↗
PubMed1983

Structural and biochemical characterisation of the paraflagellar rod of Crithidia fasciculata.

The trypanosomatid Crithidia fasciculata possesses an intraflagellar structure known as the paraflagellar or paraxial rod which runs from a point 1 to 2 micrometer distal to the basal body to the flagellar tip. In longitudinal section the paraflagellar rod was composed of three "sets" of parallel filaments arranged in a lattice. In cross section it consisted of two electron dense "plaques", one near the flagellar membrane, the other near the axoneme, separated by 6 to 7 fibrous elements. The position of the paraflagellar rod in relation to the axonemal central pair remained static along the length of the flagellum and was the same in all flagella examined. The paraflagellar rod was anchored to the axoneme by a regular array of 5 to 7 nm diameter links. These rod/axoneme links were sensitive to trypsin digestion enabling the rod to be separated from the axoneme. SDS-polyacrylamide gel electrophoresis (SDS-PAGE) demonstrated that the paraflagellar rod consisted mainly of two proteins, PFR1 (76 000 Daltons) and PFR2 (68 000 Daltons). The isoelectric points of these two proteins were remarkably similar. A PFR-enriched fraction was obtained by prolonged dialysis of demembranated flagella against a low concentration buffer. The paraflagellar rod and the central pair of singlet microtubules went into solution, leaving only the outer doublets intact. The relevance of these results to the study of the role of the paraflagellar rod in flagellar motility were discussed.

Animals↗
PubMed1981

Interference effects in recalling movements.

In two experiments, the interaction of location and distance cues in the recall of pre-selected movements was investigated. In Expt 1, separate groups of subjects were required to remember either ther terminal location of, or the distance moved during, a criterion movement pre-selected within a 30 cm response region. Following either a 5 s or 30 s unfilled retention interval, subjects were required to recall the criterion movement using the particular movement cue (i.e. location or distance) in question. In Expt 2, a similar procedure was used, except that recall of the criterion movement followed either a 5 s or a 20 s unfilled, or a 20 s filled (backward counting) retention interval. Systematic manipulation of both the direction and magnitude of the starting position for recall movements revealed the subjects were unable to make the movement uninfluenced by the "unattended' movement cue. The interfering effect of this irrelevant cue was independent of the ongoing activity during the retention interval. The results suggest that memory for preselected movements is based on a combination of the two movement cues generated during production of the criterion movement.

Cues↗