Crystal structure of SV40 large T-antigen bound to p53: interplay between a viral oncoprotein and a cellular tumor...

Area of Science:

• Molecular Biology
• Virology
• Structural Biology

Background:

• Simian Virus 40 (SV40) large T-antigen (LTag) is crucial for viral replication and cellular transformation.
• LTag interacts with cellular tumor suppressors, notably p53, to inhibit its function.
• p53 acts as a critical "guardian of the genome" by regulating cell cycle arrest and apoptosis.

Purpose of the Study:

• To elucidate the structural basis of the interaction between SV40 LTag and human p53.
• To understand how LTag binding affects p53 conformation and function.
• To investigate the impact of the p53-LTag complex on LTag's helicase activity.

Main Methods:

• Determined the crystal structure of the Simian Virus 40 large T-antigen (LTag) in complex with p53.
• Employed structure-guided mutagenesis of LTag and p53 residues.
• Assessed p53's effect on LTag helicase function through direct complex formation assays.

Main Results:

• Revealed an unexpected hexameric complex where LTag binds six p53 monomers.
• Demonstrated LTag binding induces significant conformational changes in p53's DNA-binding domain via a "methionine switch".
• Showed LTag occupies the p53 DNA-binding surface, likely preventing functional p53 tetramer formation and inhibiting LTag helicase activity.

Conclusions:

• The crystal structure provides a detailed molecular mechanism for p53 inhibition by SV40 LTag.
• LTag binding disrupts p53's DNA-binding capacity and tetramerization, compromising its tumor suppressor role.
• p53 directly inhibits LTag helicase activity, indicating a mutual regulatory interaction within the complex.