Protein disk of tobacco mosaic virus at 2.8 A resolution showing the interactions within and between subunits.

Protein subunits in the two layers of the disk of tobacco mosaic virus have very similar conformations. Much of the bonding between subunits is polar, including salt-bridge systems. Arginine residues play a prominent part here and elsewhere. Interactions within each layer involve groups whose contacts can be adjusted to allow the transition from disk to virus helix. Aromatic clusters within each molecule are linked in a hydrophobic girdle encircling each ring.