Protein engineering using bacteriophage T4 foldon
Vadim V. Mesyanzhinov

The T4 fibritin is a homotrimer that contains the N-terminal domain responsible for attachment to the phage particle and for the collar formation. The non-helical N-terminal part of 45 residues represents a new protein fold that tightly interacts with the downstream coiled-coil segment forming a single domain. The atomic structure of the N-terminal domain of fibritin was fitted to cryo-electron microscopy 3D reconstruction image of bacteriophage T4 with aim to understand the detailed structure of the viral collar/whisker complex.
The central domain forms a 500 Å long segmented coiled-coil structure, and the C-terminal ‘foldon’ domain is essential for proper folding and trimerization of the molecule. The T4 foldon has a ?-annulus like structure formed by last 30 C-terminal residues from each of the trimer subunits. The foldon residues form extensive hydrophobic and polar interactions within and between subunits. The role of foldon as a folding nucleus and its stabilizing action have been used recently to design several chimera proteins including the T4 phage fibrous proteins, short collagen fragments, human adenovirus type 5 fiber, and a stable trimeric form of a 140 kD protein of HIV-1. Such de novo engineered proteins can be used for a variety of applications, including the study of receptor-ligand recognition.
In current work, the nine residues of T4 foldon amino acid sequence was randomized, and we have selected the multiple residue mutants that direct assembly of two-stranded coiled coil structure.