ATP-dependent simian virus 40 T-antigen-Hsc70 complex formation

Area of Science:

• Molecular Biology
• Virology
• Oncology

Background:

• Simian virus 40 large T antigen (SV40 T-ag) is a key oncoprotein driving viral replication and cellular transformation.
• SV40 T-ag possesses a J domain crucial for its functions, interacting with heat shock cognate 70 kDa protein (Hsc70), a cellular chaperone.
• The precise nature of the SV40 T-ag and Hsc70 interaction, whether direct or indirect, remained unclear.

Purpose of the Study:

• To elucidate the direct binding interaction between SV40 T-ag and Hsc70.
• To characterize the binding stoichiometry, affinity, and nucleotide dependency of the SV40 T-ag–Hsc70 complex.
• To identify domains within SV40 T-ag and Hsc70 critical for their association.

Main Methods:

• Direct binding assays to determine stoichiometry and dissociation constants.
• ATP hydrolysis assays to assess nucleotide dependency.
• Analysis of T-ag fragments and yeast Hsc70 homologues to map interaction domains.

Main Results:

• SV40 T-ag directly binds Hsc70 with a 1:1 stoichiometry (Kd = 310 nM Hsc70).
• Complex formation is ATP hydrolysis-dependent at Hsc70's active site (Kd = 0.16 microM ATP) but independent of T-ag's ATP binding site.
• A J-domain fragment of T-ag formed a transient, not stable, complex; stable association requires multiple domains from both proteins.

Conclusions:

• The SV40 T-ag–Hsc70 interaction is specific and requires contributions from multiple domains of both proteins.
• This study provides the first evidence of nucleotide requirement for SV40 T-ag and Hsc70 association.
• Findings establish a foundation for studying chaperone-dependent tumorigenesis mediated by SV40 T-ag.