Immunological analysis of a glycoprotein (contact sites A) involved in intercellular adhesion of dictyostelium discoideum

Abstract

We have prepared antisera in rabbits to the "contact sites A" glycoprotein (gp80) purified from Dictyostelium discoideum. IgG isolated these antisera reacts with a number of different proteins in D discoideum lysates, as analyzed by immune precipitation and by antibody staining of gel electropherograms transferred to nitrocellulose. blocking experiments indicate that this cross-reactivity reflects the presence of common antigeneic determinants on gp80 and other cellular proteins, rather than the presence of extraneous antibodies in the antisera. The spectrum of reactive proteins is different at different stages of development. In particular, gp80 itself is synthesized only for a restricted period during the cell aggregation phase. The protein persists throughout development and can be detected in spores. Anti-gp80 Fab fragments bind to the surface of developing D discoideum cells and specifically block their developmentally regulated adhesion. After absorption with vegetative cells, the IgG stains only gp80 and (to a lesser extent) one other band in lysates of aggregation-competent cells. The absorbed antibodies also can block adhesion. Several proteins that appear late in development also are stained by the absorbed IgG.

Mutations affecting a surface glycoprotein, gp80, of Dictyostelium discoideum.

“…80,000 daltcns (gp8O) (9,10). Likewise, rabbit antibodies prepared against purified gp8O have been found to block EDTA-resistant adhesion (12). gp8O is undetectable during the first few hours of development and is synthesized and accumulates between 8 and 14 h of development coordinately with the acquisition of EDTAresistant adhesion (12,14).…”

“…Likewise, rabbit antibodies prepared against purified gp8O have been found to block EDTA-resistant adhesion (12). gp8O is undetectable during the first few hours of development and is synthesized and accumulates between 8 and 14 h of development coordinately with the acquisition of EDTAresistant adhesion (12,14). For these reasons it is thought that gp8O may play a direct role in the mechanism of cell-cell adhesion in developed D. discoideum.…”

“…Rabbit serum prepared against purified gp8O reacts not only with gp8O but with several other proteins, apparently due to the presence of shared antigenic determinants (11,12). A few of these antigenic proteins are present in vegetative cells and exhaustive absorption of this serum with vegetative cells removes some but not all immunological reactivity to gp80 (11).…”

A monoclonal antibody that interferes with the post‐aggregation adhesion of Dictyostelium discoideum cells

“…Many glycoproteins carry the modB sensitive glycoconjugate and the TKI epitope apparently delineates a small number of proteins within this class. Indirect evidence exists that surface carbohydrates participate in the cell-cell adhesion of D. discoideum cells [23,30,3941]. However, inhibition of adhesion by TKl does not necessarily implicate the TKlepitope since the antibody might interfere sterically with protein moieties on the relevant antigen(s) that are involved in adhesion.…”

“…The adhesion is mediated by homophilic interaction of contact site A (csA) molecules via peptide regions near the amino terminus . The N-carbohydrate residues are also essential for adhesion [16,23,24].…”