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B A Cunningham

Publications and source records attributed to B A Cunningham.

At least 127 records · Page 7Linked to original sources
PubMed1975

The covalent and three-dimensional structure of concanavalin A. II. Amino acid sequence of cyanogen bromide fragment F3.

The amino acid sequence of the COOH-terminal CNBr fragment, F3 (residues 130 to 237), of concanavalin A has been established, completing the determination of the covalent structure of this lectin. Analysis of the chemical sequence showed that the distribution of charged residues is generally more dense in the NH2-terminal half of the polypeptide chain than in the COOH-terminal portion and that in the latter region there is a linear stretch composed of many hydrophobic residues. Correlation with x-ray crystallographic results indicates that the hydrophobic region is located in the interior of the molecule, and that it forms a part of a deep cavity which is the binding site for the inhibitor, beta-(o-iodophenyl)-D-glucopyranoside. In conjunction with the three-dimensional structure, the amino acid sequence reported here provides new data for analysis of variables involved in predicting the three-dimensional folding of proteins from the primary structure. The sequence of concanavalin A is the first determined for a lectin and it serves as a reference structure for comparisons with other lectins.

Amino Acid Sequence↗
PubMed1975

The covalent and three-dimensional structure of concanavalin A. III. Structure of the monomer and its interactions with metals and saccharides.

The three-dimensional structure of the lectin concanavalin A (Con A) has been determined at 2.0-A resolution by x-ray diffraction analysis. The protomers are ellipsoidal domes of dimensions 42 times 40 times 39 A. Folding of the polypeptide backbone is dominated by the presence of two antiparallel pleated sheets, a twisted sheet of seven strands passing through the center of the molecule and a bowed sheet of six strands which forms the back surface of the monomer. Manganese and calcium ions bind to the protein at adjoining sites to form a binuclear complex of two octahedra sharing a common edge. The ligands for each metal ion are four groups from the NH2-terminal region of the protein and 2 water molecules. The binding site for the inhibitor beta-(o-iodophenyl)-D-glucopyranoside is in a deep cavity which contains distinct hydrophobic and hydrophilic binding subsites. Studies of the binding of beta-(o-iodophenyl)-D-glucopyranoside to Con A in the crystalline state and in solution have indicated that the binding behavior of the protein is somewhat different in the two states.

Amino Acid Sequence↗
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↗
PubMed1973

Concanavalin A derivatives with altered biological activities.

Chemical derivatization of tetrameric concanavalin A (Con A) with succinic anhydride or acetic anhydride converts the protein to a dimeric molecule without altering its carbohydrate-binding specificity. At low concentrations, the dose-response curves for the mitogenic stimulation of mouse spleen cells by native Con A and succinyl-Con A are similar. Above lectin concentrations of 10 mug/ml, however, the response to Con A is diminished, while that for succinyl-Con A does not decrease until much higher doses are reached. We have attributed this difference mainly to the higher rate of cell death induced by the native Con A molecule. Con A also shows a greater capacity than succinyl-Con A to agglutinate sheep erythrocytes and to inhibit cap formation by immunoglobulin receptors on spleen cells. Moreover, at low concentrations, Con A induced its glycoprotein receptors to form caps, but succinyl-Con A did not induce cap formation. Addition of antibodies directed against Con A to succinyl-Con A bound on cells restored the properties of agglutination, inhibition of immunoglobulin receptor cap formation, and induction of cap formation by Con A receptors. Similar results have been obtained for acetyl-Con A. These data suggest that the altered biological activities of succinyl-Con A and acetyl-Con A are attributable to their reduced valence.

Acetates↗
PubMed1972

2 -Microglobulin--a free immunoglobulin domain.

Analysis of the primary structure of beta(2)-microglobulin indicates that this human protein is homologous in sequence to the constant portion of immunoglobulin light chains (C(L)), and to the homology regions (C(H)1, C(H)2, and C(H)3) of the constant portion of gamma1 (heavy) chains of immunoglobulin G. Homology with the C(H)3 region is particularly striking. No convincing homology could be demonstrated by similar comparisons with the variable regions of immunoglobulin light and heavy chains. beta(2)-Microglobulin contains an intrachain disulfide loop of 57 amino-acid residues that is similar in size to disulfide loops found in the constant regions of immunoglobulin G. These findings suggest that beta(2)-microglobulin is a free immunoglobulin domain, possibly serving an effector function similar to that of the C(H)3 domain of gamma1 chains of immunoglobulin G.

Amino Acid Sequence↗
PubMed1972

The covalent and three-dimensional structure of concanavalin A.

The tentative amino-acid sequence and three-dimensional structure of the lectin concanavalin A have been determined. The amino-acid sequence, which was determined chemically, contains 238 residues. The sequences of three short stretches were assigned on the basis of x-ray crystallographic data. Interpretation of an electron density map at 2-A resolution indicates that the predominant structural element is extended polypeptide chain arranged in two anti-parallel pleated sheets or beta-structures. Residues not included in the beta-structures are arranged in regions of random coil. One of the pleated sheets contributes extensively to the interactions among the monomers to form both dimers and tetramers. The positions at which Mn(2+), Ca(2+), and saccharide are bound to the protein, and the point of cleavage for the formation of the naturally occurring fragments A(1) and A(2), have been tentatively assigned. Both metal-binding sites are at least 20-A removed from the position at which saccharides are bound. The saccharide-binding site is a deep pocket of approximately 6A x 7.5A x 18A, the inner portion of which is occupied by hydrophobic residues.

Amino Acid Sequence↗
PubMed1971

Unusual fragments in the subunit structure of concanavalin A.

Gel electrophoresis in sodium dodecyl sulfate and gel filtration in guanidine. HCl indicate that native concanavalin A contains several molecular species. An intact subunit of molecular weight 27,000 has been purified from this mixture. In addition, three fragments of the intact subunit have been isolated and characterized. A working model of the concanavalin A molecule has been constructed based on pairings of the intact subunit and of subunits consisting of fragments.

Amino Acid Sequence↗