Cloning, purification, and preliminary characterization by circular dichroism and NMR of a carboxyl-terminal domain of the bacteriophage P22 scaffolding protein.

Assembly of double-stranded DNA viruses and bacteriophages involves the polymerization of several hundred molecules of coat protein, directed by an internal scaffolding protein. A 163-amino acid carboxyl-terminal fragment of the 303-amino acid bacteriophage P22 scaffolding protein was cloned, overexpressed, and purified. This fragment is active in procapsid assembly reactions in vitro. The circular dichroism spectrum of the fragment, as well as the 1D-NMR and 15N-1H HSQC spectra of the uniformly-labeled protein, indicate that stable secondary structure elements are present. Determination of the three dimensional packing of these elements into the folded scaffolding protein fragment is underway. Structure-based drug design targeted at structural proteins required for viral assembly may have potential as a therapeutic strategy.