Identification of Structural Elements Involved in the Interaction of Simian Virus 40 Small Tumor Antigen with Protein Phosphatase 2A

• Published in: The Journal of biological chemistry 1998-12, Vol.273 (52), p.35339-35346
• Main Authors: Mateer, S C, Fedorov, S A, Mumby, M C
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Antigens, Polyomavirus Transforming - genetics; Antigens, Polyomavirus Transforming - metabolism; Binding Sites; Circular Dichroism; Molecular Sequence Data; Mutation; Peptide Fragments - drug effects; Peptide Fragments - metabolism; Phosphoprotein Phosphatases - antagonists & inhibitors; Phosphoprotein Phosphatases - metabolism; Protein Binding; Protein Conformation; Protein Phosphatase 2; Sequence Homology, Amino Acid; Simian virus 40; Simian virus 40 - immunology; Zinc - pharmacology
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.273.52.35339

SV40 small tumor antigen (small-t) was used as a model to identify structural elements involved in the interactions between regulatory proteins and protein phosphatase 2A (PP2A). Using mutant proteins and synthetic peptides, we identified a small domain within small-t that is a major site for interaction with the dimeric form of PP2A. A series of small-t truncation mutants identified a region surrounding the first of two conserved cysteine clusters that was critical for interaction with PP2A. These mutants also identified additional regions of small-t that contribute to high affinity interaction. Deletion of residues 110–119, which encompass the first cysteine cluster, resulted in a protein that failed to bind to PP2A. Synthetic peptides that contained residues 105–122 of small-t blocked binding of small-t to PP2A. These peptides also inhibited the phosphatase activity of PP2A in a manner analogous to full-length small-t. The active small-t peptides adopt a β-strand structure that was essential for high affinity interaction with the PP2A dimer. Based on circular dichroism measurements, the same cysteine cluster-containing peptides that bind to PP2A also interact with zinc. Interaction with zinc required the conserved cysteines but was not required for interaction with PP2A.