Structural puzzles in virology solved with an overarching icosahedral design principle

Viruses have evolved protein containers with a wide spectrum of icosahedral architectures to protect their genetic material. The geometric constraints defining these container designs, and their implications for viral evolution, are open problems in virology. The principle of quasi-equivalence is currently used to predict virus architecture, but improved imaging techniques have revealed increasing numbers of viral outliers. We show that this theory is a special case of an overarching design principle for icosahedral, as well as octahedral, architectures that can be formulated in terms of the Archimedean lattices and their duals. These surface structures encompass different blueprints for capsids with same numbers of structural proteins, as well as for capsid architectures formed from a combination of minor and major capsid proteins, and are conserved within viral lineages. They also apply to other icosahedral structures in nature, and offer alternative designs for man-made materials and nanocontainers in bionanotechnology

Nature’s Favorite Building Block: Deciphering the HK97-like Fold of Bacteriophage P22 Coat Protein.

Bacteriophage P22, which infects Salmonella enterica serovar Typhimurium, is a paradigm for the assembly of tailed bacteriophage and Herpesviridae (Teschke and Parent, 2010). For many dsDNA viruses, including bacteriophage P22, chemically identical coat proteins occupy non-identical hexon and penton sites in the icosahedron. This relies on coat protein plasticity, as the subunits must undergo conformational switching during procapsid assembly and virion maturation. Bacteriophage P22 coat protein shares a common HK97-like fold with many dsDNA viruses, however it has an additional genetically inserted domain. Capsids using the HK97-like fold range in size from ~24 nm to ~145 nm in diameter (Bamford et al., 2005). The viruses that use this building block have evolved specialized ways to manage folding, assembly, stabilization, and cell infection. Biochemical, structural, and genetic studies on P22 coat protein provide clues about the HK97-like fold, which likely represents the absolute most abundant fold in the biosphere

Molecular determinants for dsDNA translocation by the transcription-repair coupling and evolvability factor Mfd

Transcription-repair coupling factors (TRCFs) are large ATPases that mediate the preferential repair of the transcribed DNA strand. Here the authors reveal the cryo-EM structure of DNA-bound Mfd, the bacterial TRCF, and provide molecular insights into its mode of action