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Lysosomal enzymes possess a common antigenic determinant in the cellular slime mold, Dictyostelium discoideum
Abstract:
Antisera have been prepared against two lysosomal enzymes of the cellular slime mold, Dictyostelium discoideum. The two purified enzyme preparations used for immunization, N-acetylglucosaminidase and beta-glucosidase-1, show no cross-contamination with each other and no significant contamination by other lysosomal enzymes. However, antisera raised against either enzyme bind equally well to seven different lysosomal enzymes and show no preference for the enzyme against which they were raised. A total of 10 different antisera have been examined and all show similar results. Preadsorption of antisera with either purified enzyme removes all antibody activity against the other enzyme. Evidence is presented which indicates that the same species of antibodies are responsible for the precipitation of seven lysosomal enzymes. These data are discussed in terms of the proposal that the antigen that is shared by the lysosomal enzymes is a post-translational modification of the enzyme proteins. We have sought to further characterize the distribution of this common antigen among cellular proteins. We show that N-acetylglucosaminidase and beta-glucosidase-1 represent less than 5% of the total common antigen containing proteins in the cell. Precipitation of 35S-labeled cellular proteins from vegetative cells indicates that as much as 15-30% of the total cell protein may possess the common antigen. Preadsorption experiments confirm that all of the proteins immunoprecipitated in these experiments are recognized by the same antibodies that precipitate the lysosomal enzyme activities. Most of the labeled proteins are secreted into the medium along with the lysosomal enzyme activities during axenic growth. During the developmental phase of the life cycle of Dictyostelium, the total amount of the common antigen decreases about 2-fold relative to total cell protein. However, the synthesis of antigenic proteins continues throughout most of development.
Insights
Antisera against Dictyostelium discoideum lysosomal enzymes revealed a shared antigen, likely a post-translational modification, present in up to 30% of cellular proteins. This common antigen
Area of Science:
- Cell Biology
- Biochemistry
- Molecular Biology
Background:
- Lysosomal enzymes in Dictyostelium discoideum are crucial for cellular processes.
- Previous studies suggested potential shared characteristics among these enzymes.
Purpose of the Study:
- To investigate the antigenic properties of Dictyostelium discoideum lysosomal enzymes.
- To identify the nature and distribution of a potential common antigen among these enzymes and other cellular proteins.
Main Methods:
- Preparation and characterization of antisera against purified N-acetylglucosaminidase and beta-glucosidase-1.
- Immunoprecipitation assays using labeled cellular proteins.
- Preadsorption experiments to confirm antibody specificity.
Main Results:
- Antisera against individual lysosomal enzymes cross-reacted with multiple other lysosomal enzymes, indicating a shared antigenic determinant.
- This common antigen is not limited to lysosomal enzymes, with up to 30% of total cellular proteins potentially possessing it.
- The antigen is found in secreted proteins and its relative abundance decreases during Dictyostelium development, though synthesis continues.
Conclusions:
- A common antigen, likely a post-translational modification, is shared among Dictyostelium discoideum lysosomal enzymes and other cellular proteins.
- This antigen's distribution suggests a broader role beyond lysosomal function.
- Its dynamic changes during development hint at regulatory mechanisms controlling its expression.