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Biomedical subjects

G M Edelman

Publications and source records attributed to G M Edelman.

At least 307 records · Page 17Linked to original sources
PubMed1975

The covalent and three-dimensional structure of concanavalin A. IV. Atomic coordinates, hydrogen bonding, and quaternary structure.

The coordinates of the individual non-hydrogen atoms of the lectin concanavalin A have been determined from the molecular model at 2.0-A resolution and have been adjusted to make them consistent with the known stereochemistry of the constituent amino acid residues. From the coordinates, an analysis has been made of all intra- and intersubunit interactions in the molecule, yielding a description of the hydrogen-bonded structure of the monomer, including two extensive pleated sheet structures and other features of the folding of the polypeptide chain. The description of the noncovalent bonding is extended to include the interactions involved in stabilization of the dimeric and tetrameric structures of the molecule. The complete description of the molecular structure provides a basis for analysis of the biological activities of concanavalin A.

Binding Sites↗
PubMed1975

Structure and function of concanavalin A.

Lectins have been extensively used to analyze a variety of fundamental processes in cell biology. In conjuntion with our studies on the cell surface and mitosis, we have determined the amino acid sequence and three-dimensional struction of concanavalin A (Con A), the mitogenic lectin from the jack bean. Knowledge of the structure has been helpful in interpreting experiments on lymphocyte mitogenesis and the effects of Con A on cell surface receptor mobility. Con A subunits for molecular weight 25,500 are folded into dome-like structures of maximum dimensions 42 times 40 times 39 A. The domes are related by 222 symmetry to form roughly tetrahedral tetramers. Each subunit contains two large antiparallel pleated sheets, and subunits are joined to form dimers and tetramers by interactions involving one of these pleated sheets. We have examined the binding of a variety of carbohydrates to Con A and have obtained preliminary data which suggest that there are differences in the saccharide-binding behavior of Con A in solution and in the crystalline state. Dimeric chemical derivatives of Con A have been prepared and shown to have biological activities different from those of the native tetrameric protein. Under different conditions, native Con A exhibits two antagonistic activities on the lymphoid cell surface: the induction of cap formation by its own receptors and the inhibition of the mobility of a variety of receptors, including its own receptors. The dimeric derivative, succinyl-Con A, is just as effective a mitogen as the native lectin, but it lacks the ability to modulate cell surface receptor mobility. The data suggest that neither extensive immobilization of cell surface receptors nor cap formation is required for cell stimulation. Further studies on modulation of receptor translocation suggest that hypothesis that there exists a connecting network of colchicine-sensitive proteins that links receptors of different kinds and mediates their rearrangement. The degree of connectivity of this postulated network appears to be altered by changes in the state of attachment of various surface receptors to the network. Thus the network might provide the cell with a means of transmitting signals such as the stimulus for mitosis by lectins or antigens.

Amino Acid Sequence↗
PubMed1975

Functional interactions of viral and histocompatibility antigens at tumor cell surfaces.

Several lines of evidence are presented to suggest that histocompatibility antigens can be physically associated on the cell surface with viral antigens and possibly other foreign antigens. The lysis of the murine tumor cells EL4 and P388 by syngeneic cytotoxic lymphocytes was inhibited by antisera directed against the H-2 antigens on the tumor cells, consistent with the hypothesis that H-2 antigens are part of the target of the cytotoxic lymphocytes. Moreover, it was found that patching and capping of the H-2 antigens on EL4 cells resulted in the co-patching and co-capping of viral antigens as detected by antisera against Rauscher leukemia virus. Capping of H-2 antigens also resulted in co-capping of determinants detected by an antiserum to the viral protein gp69/71. On the basis of these and other observations, we propose the hypothesis that the H-2 molecules serve as adaptors that combine with viral antigens on the cell surface to form hybrid antigens containing elements of self (H-2) and non-self (virus). The adaptor-antigen complex may then be recognized by a subclass of thymus-derived (T) lymphocytes that possesses a repertoire of receptors directed against hybirds of foreign and H-2 antigens. This raises the possibility that other products of the major histocompatibility complex may have analogous functions.

Animals↗
PubMed1975

Antibodies reactive with cell surface carbohydrates.

Normal and immune sera from various animal species were fractionated on columns of Sepharose covalently coupled with the glycoprotein fetuin. Elution of the material bound to fetuin yielded low but reproducible amounts of protein, ranging from 0.02 to 0.2% of the protein mass of the input sera. This material has been identified by immunoelectrophoresis in agar and by zone electrophoresis on cellulose acetate as immunoglobulin. The Ig fractions bound and agglutinated erythrocytes of various species, and also bound to cells from various mouse tissues including heart, kidney, thymus, and spleen. In all cases, the binding was inhibited by glycoproteins such as fetuin and thyroglobulin, by a glycopeptide isolated from fetuin, and by some bacterial lipopolysaccharides. When the binding of these Ig fractions to mouse splenocytes was tested in the presence of 17 saccharides, no inhibition of binding was observed except by sialic acid, D-galactose, N-acetyl-D-glucosamine, and D-mannose, all of which showed partial inhibition. Inasmuch as these four saccharides are present on the carbohydrate moiety of fetuin, the results suggest that the isolated material is a carbohydrate-specific Ig (CS-Ig) fraction of serum capable of binding to the carbohydrate portion of cell surface receptors and glycoproteins. When bound to lymphocytes, these CS-Ig molecules induced redistribution (patching and capping) of cell surface receptors. Moreover, the CS-Ig fractions from chicken and rabbit sera were weakly mitogenic for mouse splenic lymphocytes. CS-Ig fractions are useful new reagents for studying glycoproteins and the interactions and activities of cell surface carbohydrates.

Agglutination↗
PubMed1975

Modulation of lymphocyte receptor mobility by locally bound concanavalin A.

Binding of concanavalin A (con A) to the lymphocyte surface at room temperature leads to restriction of the mobility of a variety of cell surface receptors including those from immunoglobulin (Ig), O, H-2, beta2-microglobulin, Fc receptors results in "co-capping" of Ig, H-2, theta, Fc receptors, as well as receptors for other lectins. Addition of colchicine to the cell suspensions reverses this effect and allows Con A receptors as well as other receptors to form patches and caps. Capping of Con A receptors, and beta2-microglobulin in the absence of ligands specific for these receptors. Receptors binding Limulus hemagglutinin and wax bean agglutinin, as well as those interacting with carbohydrate-specific antibodies, were partially co-capped with Con A but receptors for wheat germ agglutinin were not co-capped, excluding the possibility that restriction of receptor mobility by Con A resulted simply from cross-linkage of mobile receptors to immobilized glycoproteins (Con A receptors). Latex beads and platelets coupled to Con A were bound to lymphocytes under the same conditions as free Con A. Binding of these particles to local regions of the cell surface resulted in restriction of the mobility of those receptors that could be co-capped with free Con A. In contrast to the findings with free Con A, however, addition of colchicine resulted in capping of the bound particles but did not cause co-capping of either the unbound Con A receptors or other receptors. These findings support the hypothesis that modulation occurs via a submembranous assembly containing microtubules, and they further suggest that the transitions of this assembly induced locally by Con A may be propagated via cooperative processes.

Animals↗
PubMed1975

Modulation of lymphocyte mitogenesis.

Comparisons of the stimulation of normal lymphocytes and lymphoma cells by tetrameric concanavalin a (Con ta) and dimeric succinyl-Con A suggest that both stimulatory and inhibitory signals operate to modulate mitogenesis. Synergistic effects can be obtained for the stimulatory event using lectins, phorbol esters, and calcium ionophores, all of which are independently mitogenic for lymphocytes. The inhibitory effects of high doses of Con A could be mimicked by the simultaneous addition of the phorbol ester and Con A under conditions in which both reagents are optimally mitogenic when used alone. No inhibition of stimulation was found, however, when succinyl-Con A was used with phorbol ester under the same conditions. Moreover, when lymphocytes were cultured with Con A in the presence of succinyl-Con A, the inhibitory effect of the native lectin was seen at lower doses than in the absence of the derivative. These observations suggest that the stimulatory and inhibitory portions of the dose-response curve can be manipulated independently and may be mediated by two distinct signals. It is likely the signal for the inhibition of cell proliferation is regulated by the same cell surface modulating assembly that controls the mobility of cell surface receptors.

Animals↗
PubMed1975

Inhibition by colchicine of the mitogenic stimulation of lymphocytes prior to the S phase.

Colchicine, vinblastine, and vincristine inhibit the mitogenic stimulation of lymphocytes by concanavalin A as measured by the incorporation of [3H]thymidine and the appearance of blast cells. The inhibitory effect of colchicine could not be accounted for by diminution in cell viability or by metaphase arrest of mitosis in the stimulated cells. Moreover, the inhibition of [3H]thymidine incorporation was not due to blockage of thymidine transport or inhibition of DNA synthesis inasmuch as addition of colchicine had no effect on cells in the S phase of the cell cycle. The time of inhibition was correlated with the kinetics of cellular commitment to lectin activation and the kinetic data indicated that colchicine blocks stimulation early in the sequence of events following addition of the mitogen. These findings support the hypothesis that cytoplasmic microtubular function plays a role in the commitment of resting cells to undergo mitotic division.

Animals↗
PubMed1975

Chemical dissection of mammalian spermatozoa.

Mammalian spermatozoa have been dissected by a variety of chemical techniques to yield free heads, tails with attached midpieces, and tails without mitochondria. By brief exposure to trypsin, mouse and rat spermatozoa were cleaved at the junction of the head and the tail, while human, guinea pig and rabbit spermatozoa were cleaved by trypsin only after prior incubation with a sulphhydryl reducing agent. Treatment with acid or base cleaved spermatozoa of all species examined. In contrast, exposure of spermatozoa to 1% sarkosyl NL-97 resulted in the quantitative cleavage of mouse cells without noticeable effect on the spermatozoa of the other species. Mitochondria were removed from the midpiece of intact sperm and isolated tails by gentle shaking after treatment with reducing agents. Homogeneous populations of spermatozoan subcellular components were obtained by density gradient centrifugation. Ultrastructural analysis showed that cleavage of mouse spermatozoa by trypsin occurs at a specific location in the neck of the cell without trypsin occurs at a specific location in the neck of the cell without observable damage to other cell structures. The basal plate remained attached to the head structures. In contrast cleavage of spermatozoa by sarkosyl or acid left the basal plate attached to the spermatozoan midpiece. Sarkosyl also removed the plasma membrane and extracted mitochondrial components. Treatment with acid or base also resulted in vesiculation of the plasma membrane and dissolution of the acrosome. Molecular probes have also been used to facilitate mapping of the cell surface. Each mouse spermatozoon has about 10-7 receptors for the lectin concanavalin A. Binding of fluorescein-labelled concanavalin A indicated that the majority of the receptors is in the acrosomal region; this polar distribution was confirmed by measurement of the number of sites on purified heads and tails. In addition, the low molecular weight probe ANS bound to the plasma membrane of spermatozoa from all species examined, with immediate immobilization of the cells. Ethidium bromide bound to the spermatozoan head without affecting motility.

Animals↗
PubMed1974

Maturation of the humoral immune response in mice.

In spite of the prenatal appearance of immunoglobulin-bearing lymphocytes and theta-positive lymphocytes in the spleens of Swiss-L mice, these mice are not able to produce detectable levels of humoral antibodies in response to antigen until after 1 wk of age. Adult levels of response are not achieved until 4-8 wk of age. In the presence of bacterial lipopolysaccharides, which can substitute for or enhance T-cell function, the B cells from young Swiss-L mice were found to be indistinguishable in function from adult B cells, both with respect to the numbers of plaque-forming cells (PFC) produced in vitro in response to antigen and with respect to the kinetics of PFC induction. The spleen cells from young Swiss-L mice are significantly less sensitive than adult spleen cells, however, to stimulation by the T cell mitogens, concanavalin A (Con A) and phytohemagglutinin (PHA). Very few Con A-responsive cells could be detected at birth but the numbers increased sharply with age until 3 wk after birth. On the other hand, PHA-responsive cells could not be detected in the spleen until about 3 wk of age. The latter cells were found to respond also to Con A, but at a lower dose (1 microg/ml) than that required for the bulk of the Con A-responsive cells (3 microg/ml). The cells that respond both to PHA and to Con A appear in the spleen at about the time that Swiss-L mice acquire the ability to produce humoral antibodies, and these cells can be depleted from the spleen by the in vivo administration of antithymocyte serum. The development of humoral immune responses in these mice therefore appears to be correlated with the appearance of recirculating T lymphocytes that are responsive both to PHA and to Con A.

Age Factors↗
PubMed1974

Morphology, motility, and surface behavior of lymphocytes bound to nylon fibers.

Mouse B lymphocytes that were specifically bound to dinitrophenylated bovine serum albumin on nylon fibers exhibited continuous morphological changes, whereas bound T lymphocytes remained more or less spherical. Cinematomicrographic studies showed that the shape changes were associated with local and global movements, although the attached cells did not translocate along the fiber. Cap formation induced by anti-immunoglobulin was always found to be opposite to the point of attachment. The movements and the shape changes were prevented by cytochalasin B and colchicine. Treatment with these agents did not prevent cap formation but led to randomization of the position of the caps with respect to the fiber. Exposure to concanavalin A or attachment of cells to concanavalin A fibers prevented both movement and patch and cap formation, suggesting that cellular structures regulating the mobility of various receptors are altered by binding to concanavalin A fibers. These observations also indicate that interactions of local areas of the lymphocyte surface with certain ligands and substrates can strongly affect the movement and morphology of the entire cell.

Animals↗
PubMed1974

The kinetics of cellular commitment during stimulation of lymphocytes by lectins.

The kinetics of cellular commitment in the stimulation of lymphocytes by concanavalin A (Con A) has been analyzed by measurement of DNA synthesis, autoradiography, and histologic staining techniques. If the competitive inhibitor alpha-methyl-D-mannoside (alphaMM) is introduced into cultures of mouse spleen cells at various times after the addition of Con A, there is a gradual decrease in its capacity to inhibit the lectin-stimulated incorporation of [(3)H]thymidine. Addition of the saccharide 20 h after exposure of the cells to Con A had no effect on the level of the cellular response to the lectin. With increasing periods of contact with Con A, the percentage of blast cells and the percentage of [(3)H]thymidine-labeled blast cells increased in parallel with the total radioactive thymidine incorporated while the average number of autoradiographic grains per labeled blast cell remained relatively constant. These observations suggest that the rising level of [(3)H]thymidine incorporation results from an increase in the number of cells that respond to lectin stimulation and become refractory to inhibition with alphaMM. Once such cells become committed, they synthesize DNA at a rate independent of the length of exposure to the lectin. The combined results indicate that mouse splenic lymphocytes are heterogeneous in their capacities to respond to Con A and that different cells require different induction periods to be stimulated.

Animals↗