Virtuelle (Nano) Welten: PDB Molecule of the Month 47: SV40

The Amazing T-antigen

SV40 packs all of its functional needs into one remarkable, multifunctional protein. The T-antigen is composed of several functional parts, connected by flexible linkers. Structures of the three major pieces are available in the PDB. At one end, a helicase domain assembles with several other copies of the protein to form a six-fold ring (shown on the left from PDB entry 1n25). The hole is just big enough to encircle a DNA double helix. The central domain (PDB entry 1tbd) has a small patch, shown here in green, that binds specifically to the regulatory region in the SV40 genome, anchoring the T-antigen complex in the proper place. The third domain interacts with cellular proteins, directing the various stages in the viral life cycle. It is shown here on the right bound to the Rb protein, shown in red (PDB entry 1gh6). In the cell, twelve copies of the protein assemble around the DNA to form a long tube, as shown at the bottom.

Simian Virus 40

The Amazing T-antigen