Keeping It Together: Structures, Functions, and Applications of Viral Decoration Proteins

Abstract

Decoration proteins are viral accessory gene products that adorn the surfaces of some phages and viral capsids, particularly tailed dsDNA phages. These proteins often play a “cementing” role, reinforcing capsids against accumulating internal pressure due to genome packaging, or environmental insults such as extremes of temperature or pH. Many decoration proteins serve alternative functions, including target cell recognition, participation in viral assembly, capsid size determination, or modulation of host gene expression. Examples that currently have structures characterized to high-resolution fall into five main folding motifs: β-tulip, β-tadpole, OB-fold, Ig-like, and a rare knotted α-helical fold. Most of these folding motifs have structure homologs in virus and target cell proteins, suggesting horizontal gene transfer was important in their evolution. Oligomerization states of decoration proteins range from monomers to trimers, with the latter most typical. Decoration proteins bind to a variety of loci on capsids that include icosahedral 2-, 3-, and 5-fold symmetry axes, as well as pseudo-symmetry sites. These binding sites often correspond to “weak points” on the capsid lattice. Because of their unique abilities to bind virus surfaces noncovalently, decoration proteins are increasingly exploited for technology, with uses including phage display, viral functionalization, vaccination, and improved nanoparticle design for imaging and drug delivery. These applications will undoubtedly benefit from further advances in our understanding of these versatile augmenters of viral functions.

Journey to the center of the phage; revealing the ejectosome of Pectobacterium bacteriophage ΦM1

“…Similar functions have been observed in the decoration proteins of other DNA phages, e.g. phage N4 gp17, phi29 gp8.5, bacteriophage T5 pb10 and T4 HOC (37)(38)(39)(40).…”

Bacteriophage ICP1: A Persistent Predator of Vibrio cholerae

“…Similar to tail assembly, we can predict ICP1’s capsid assembly pathway from other well-characterized phages ( 31 – 37 ). The procapsid is assembled from coat proteins (Gp122), which are guided by scaffolds (Gp124) into place around the portal (Gp127) through which the concatemerized genomes are packaged by the terminase.…”

“…Finally, tail fibers (Gp69, Gp70, Gp93) are added to the baseplate to form a complete tail, which attaches to a capsid at the neck protein after DNA packaging. Similar to tail assembly, we can predict ICP1's capsid assembly pathway from other wellcharacterized phages (31)(32)(33)(34)(35)(36)(37). The procapsid is assembled from coat proteins (Gp122), which are guided by scaffolds (Gp124) into place around the portal (Gp127) through which the concatemerized genomes are packaged by the terminase.…”

Viral Nanoparticles‐Mediated Delivery of Therapeutic Cargo

“…[ 121 ] The phage HK97 coat protein fold is prevalent across dsDNA viruses. [ 122 ] Additionally, its negatively charged surface naturally prevents interactions with negatively charged cell membranes. Specifically, it interacts with mammalian cell surface proteins due to its larger surface, higher stability, more accessible binding sites, and greater capacity for therapeutic loading molecules.…”