Predicted structure of tail-fiber proteins of T-even type phages.

The sequences of the tail fiber protein 36 of the phages T4, T2, K3, and Ox2 were analyzed for homologies and for folding patterns using structure prediction methods. No repeating motif was found. A model for the fiber structure is proposed in which beta-strands of about 6 amino acids are separated by turns. In the beta-strand, hydrophobic amino acids are found alternating with hydrophilic ones. Such amphipathic beta-strands can be stabilized by dimer formation. The dimerization occurs in a parallel fashion so that both N-termini are at one end of the dimer. This structure represents a rigid fiber. Our model is consistent with electron microscopic data and electron diffraction patterns for the T4 tail fiber. The observation that all fiber components are found as dimers supports our model. Sequences of the receptor recognition proteins 38 of T-even type phages reveal an architecture different from the architecture of the fiber proteins 36 and 37 of these phages.