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Partial characterization of the MPM-2 phosphoepitope
1Department of Cell Biology, Neurobiology, and Anatomy, The Ohio State University, Columbus, Ohio, 43210, USA.
Abstract:
The MPM-2 monoclonal antibody recognizes a distinctive group of proteins that are associated with structural components of the mitotic apparatus. These proteins become phosphorylated and MPM-2 reactive during M-phase and appear to be required for both the onset and completion of M-phase. Based upon the analysis of reported MPM-2 reactive sequences, we have developed a model for the essential elements that comprise the MPM-2 epitope. This model was tested by employing a series of synthetic phosphopeptides. We show here that a 14 amino acid synthetic phosphopeptide, derived from a potential MPM-2 site on human DNA topoisomerase II, is recognized by the MPM-2 antibody. This phosphopeptide was sufficient to compete for MPM-2 antibody recognition of (1) an isolated native mitotic MPM-2 antigen on dot blots, (2) proteins on immunoblots of mitotic cell lysates, and (3) specific immunostaining of mitotic cells. These results indicated that the topoisomerase peptide contained all of the essential elements of the MPM-2 epitope. By substituting selected amino acids with alanine, we were able to examine the contribution of different amino acids to the binding between the MPM-2 antibody and the epitope. Changing the amino acid that was adjacent to the phosphorylated threonine residue on the C-terminal side (the +1 position) had no effect on MPM-2 antibody binding. However, substitution of aromatic amino acids at either the -2 or +2 positions reduced antibody recognition. The aromatic amino acid at the -2 position appeared to be the most critical residue of those tested that influenced antibody binding. These results provide information required for the molecular definition of the MPM-2 epitope and should aid in the identification of potential MPM-2 reactive sites on other mitotic phosphoproteins.
Insights
The MPM-2 antibody recognizes specific phosphorylated proteins essential for cell division (M-phase). Researchers identified a key phosphopeptide from DNA topoisomerase II that defines the MPM-2 epitope, aiding in identifying other mitotic phosphoproteins.
Area of Science:
- Cell Biology
- Molecular Biology
- Immunology
Background:
- The MPM-2 monoclonal antibody targets proteins crucial for the cell division (mitotic) apparatus.
- These proteins are phosphorylated and recognized by MPM-2 during M-phase, indicating their role in cell division progression.
- Understanding the MPM-2 epitope is key to identifying and studying these critical mitotic phosphoproteins.
Purpose of the Study:
- To develop a model for the essential elements of the MPM-2 epitope.
- To validate this model using synthetic phosphopeptides.
- To elucidate the specific amino acid requirements for MPM-2 antibody binding.
Main Methods:
- Analysis of known MPM-2 reactive sequences to propose an epitope model.
- Synthesis and testing of a 14 amino acid phosphopeptide from human DNA topoisomerase II.
- Competition assays using dot blots, immunoblots, and immunostaining to assess antibody recognition.
- Alanine substitution analysis of the phosphopeptide to determine critical amino acid residues.
Main Results:
- A synthetic phosphopeptide from DNA topoisomerase II was recognized by the MPM-2 antibody.
- This phosphopeptide effectively competed for MPM-2 binding to native antigens and cellular proteins.
- Aromatic amino acids at the -2 and +2 positions relative to the phosphorylated residue were critical for antibody binding, with the -2 position being most important.
Conclusions:
- The synthetic topoisomerase II phosphopeptide contains the essential elements of the MPM-2 epitope.
- The study provides a molecular definition of the MPM-2 epitope, highlighting the importance of specific aromatic residues.
- These findings will facilitate the identification of other MPM-2 reactive sites on mitotic phosphoproteins.