Structure Based Models Suggest That J-Domains Within Polyomavirus T-Antigens Help Regulate p53 Binding During Viral DNA Replication

The T-antigens (T-ags) encoded by Polyomaviruses (PyV) have multiple roles during viral DNA replication. There is still, however, considerable uncertainty regarding the functions of T-ag during different stages of DNA replication and the regulation of this process. As examples, how cell cycle dependent phosphorylation of a single threonine residue regulates PyV DNA replication has not been established, the purpose of the N-terminal J-domain during DNA replication in vivo is not understood and it is not clear how p53 is displaced from the surface of T-ag. The failure to resolve these issues is due, in part, to previous structural studies utilizing individual domains of T-ag rather than full-length T-ag molecules. Therefore, we have used AlphaFold3 to model the structure of full-length SV40 T-ag in the presence of a model DNA replication fork, co-factors, and phosphorylation of Thr 124. These modeling studies indicate that cell-cycle dependent phosphorylation of T-ag residue Thr 124 stabilizes a conformation in which the J-domain is located over the helicase domain. In this position, J-domain residues form multiple bonds with helicase domain residues that form the binding site for p53. Therefore, it is proposed that the SV40 J-domain (along with hsc70) has a role in the displacement of p53 from the surface of T-ag, a process that may enable the recruitment of the polymerase ⍺-primase complex and the subsequent initiation of viral DNA replication.