Templated trimerization of the phage L decoration protein on capsids.

The 134-residue phage L decoration protein (Dec) forms a capsid-stabilizing homotrimer that has an asymmetric tripod-like structure when bound to phage L capsids. The N-termini of the trimer subunits consist of spatially separated globular OB-fold domains that interact with the virions of phage L or the related phage P22. The C-termini of the trimer form a three-stranded intertwined spike structure that accounts for nearly all the interactions that stabilize the trimer.

The phage L capsid decoration protein has a novel OB-fold and an unusual capsid binding strategy.

The major coat proteins of dsDNA tailed phages (order ) and herpesviruses form capsids by a mechanism that includes active packaging of the dsDNA genome into a precursor procapsid, followed by expansion and stabilization of the capsid. These viruses have evolved diverse strategies to fortify their capsids, such as non-covalent binding of auxiliary 'decoration' (Dec) proteins. The Dec protein from the P22-like phage L has a highly unusual binding strategy that distinguishes between nearly identical three-fold and quasi-three-fold sites of the icosahedral capsid.

NMR assignments for monomeric phage L decoration protein.

Phage L encodes a trimeric 43 kDa decoration protein (Dec) that noncovalently binds and stabilizes the capsids of the homologous phages L and P22 in vitro. At physiological pH Dec was unsuitable for NMR. We were able to obtain samples amenable for NMR spectroscopy by unfolding Dec to pH 2 and refolding it to pH 4.

Mechanism of Protein Denaturation: Partial Unfolding of the P22 Coat Protein I-Domain by Urea Binding.

The I-domain is an insertion domain of the bacteriophage P22 coat protein that drives rapid folding and accounts for over half of the stability of the full-length protein. We sought to determine the role of hydrogen bonds (H-bonds) in the unfolding of the I-domain by examining (3)JNC' couplings transmitted through H-bonds, the temperature and urea-concentration dependence of (1)HN and (15)N chemical shifts, and native-state hydrogen exchange at urea concentrations where the domain is predominantly folded. The native-state hydrogen-exchange data suggest that the six-stranded β-barrel core of the I-domain is more stable against unfolding than a smaller subdomain comprised of a short α-helix and three-stranded β-sheet.