‘Let the phage do the work’: Using the phage P22 coat protein structures as a framework to understand its folding and assembly mutants

Abstract

Summary The amino acid sequence of viral capsid proteins contains information about their folding, structure and self-assembly processes. While some viruses assemble from small preformed oligomers of coat proteins, other viruses such as phage P22 and herpesvirus assemble from monomeric proteins (Fuller and King, 1980; Newcomb et al., 1999). The subunit assembly process is strictly controlled through protein:protein interactions such that icosahedral structures are formed with specific symmetries, rather than aberrant structures. dsDNA viruses commonly assemble by first forming a precursor capsid that serves as a DNA packaging machine (Earnshaw, Hendrix, and King, 1980; Heymann et al., 2003). DNA packaging is accompanied by a conformational transition of the small precursor procapsid into a larger capsid for isometric viruses. Here we highlight the pseudo-atomic structures of phage P22 coat protein and rationalize several decades of data about P22 coat protein folding, assembly and maturation generated from a combination of genetics and biochemistry.

Structural basis for scaffolding-mediated assembly and maturation of a dsDNA virus

“…S3A). Out of 21 temperature-sensitive mutations that affect the coat protein monomer folding and/or capsid assembly (25)(26)(27)), 14 are found in this domain, suggesting it plays a key role in stabilizing the monomeric coat protein and/ or the procapsid shell (Fig. S3C).…”

Unraveling the Role of the C-terminal Helix Turn Helix of the Coat-binding Domain of Bacteriophage P22 Scaffolding Protein

“…Structural studies of PCs with and without scaffolding protein have indicated scaffolding protein contact points near the strict and local 3-fold axes of the coat protein shell (the positions where three hexons or pentons meet) in these structures (25,80,81). According to current P22 coat protein models (25,29,82), this region likely corresponds largely to the N-terminal part of the protein. We have speculated from these models that negatively charged coat protein amino acids Asp-14, Glu-15, Glu-18, Glu-97, and/or possibly Asp-385 may be involved in the interaction with the positively charged Arg-293 and Lys-296 of the scaffolding protein HTH domain (49), and this idea fits well with the observation that this region undergoes a conformational change during PC maturation so that these amino acids are no longer at the interior surface (25,29).…”

Structure of P22 Headful Packaging Nuclease

“…P22 is a general transducing phage (7) and is often referred to as the representative member of the Podoviridae family of short tailed bacteriophages (8). Genome packaging in P22 has been studied mainly by genetic analysis.…”