SV40 large T antigen hexamer structure: domain organization and DNA-induced conformational changes

Curr Biol. 2002 Mar 19;12(6):472-6. doi: 10.1016/s0960-9822(02)00696-6.

Abstract

Simian Virus 40 replication requires only one viral protein, the Large T antigen (T-ag), which acts as both an initiator of replication and as a replicative helicase (reviewed in ). We used electron microscopy to generate a three-dimensional reconstruction of the T-ag hexameric ring in the presence and absence of a synthetic replication fork to locate the T-ag domains, to examine structural changes in the T-ag hexamer associated with DNA binding, and to analyze the formation of double hexamers on and off DNA. We found that binding DNA to the T-ag hexamer induces large conformational changes in the N- and C-terminal domains of T-ag. Additionally, we observed a significant increase in density throughout the central channel of the hexameric ring upon DNA binding. We conclude that conformational changes in the T-ag hexamer are required to accommodate DNA and that the mode of DNA binding may be similar to that suggested for some other ring helicases. We also identified two conformations of T-ag double hexamers formed in the presence of forked DNA: with N-terminal hexamer-hexamer contacts, similar to those formed on origin DNA, or with C-terminal contacts, which are unlike any T-ag double hexamers reported previously.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adenosine Triphosphatases / metabolism
  • Antigens, Polyomavirus Transforming / chemistry*
  • Antigens, Polyomavirus Transforming / metabolism*
  • Binding Sites
  • DNA / chemistry
  • DNA / metabolism*
  • DNA Helicases / metabolism
  • Image Processing, Computer-Assisted
  • Microscopy, Electron
  • Models, Molecular
  • Protein Conformation
  • Protein Structure, Tertiary

Substances

  • Antigens, Polyomavirus Transforming
  • DNA
  • Adenosine Triphosphatases
  • DNA Helicases