Abstract
Widespread antibiotic resistance has returned attention to bacteriophages as a means of managing bacterial pathogenesis. Synthetic biology approaches to engineer phages have demonstrated genomic editing to broaden natural host ranges, or to optimise microbicidal action. Gram positive pathogens cause serious pastoral animal and human infections that are especially lethal in newborns. Such pathogens are targeted by the obligate lytic phages of the Salasmaviridae and Guelinviridae families. These phages have relatively small ~20 kb linear protein-capped genomes and their compact organisation, relatively few structural elements, and broad host range, are appealing from a phage-engineering standpoint. In this study, we focus on portal proteins, which are core elements for the assembly of such tailed phages. The structures of dodecameric portal complexes from Salasmaviridae phage GA1, which targets Bacillus pumilus, and Guelinviridae phage phiCPV4 that infects Clostridium perfringens, were determined at resolutions of 3.3 Å and 2.9 Å, respectively. Both are found to closely resemble the related phi29 portal protein fold. However, the portal protein of phiCPV4 exhibits interesting differences in the clip domain. These structures provide new insights on structural diversity in Caudovirales portal proteins and will be essential for considerations in phage structural engineering.
Highlights
In an era of widespread antibiotic resistance, there is a need to explore alternative treatments to treat bacterial pathogenesis, such as phage therapy, in which bacteriophages are administered as therapeutic antimicrobials
Synthetic DNA was sourced from Integrated DNA Technologies (IDT), and DNA modifying enzymes and E. coli strains were sourced from New England BioLabs (NEB), unless otherwise stated
Portal Protein (PP) GA1 gp10 and phiCPV4 gp17 were recombinantly expressed in E. coli hosts and purified by column chromatography as described in the methods
Summary
In an era of widespread antibiotic resistance, there is a need to explore alternative treatments to treat bacterial pathogenesis, such as phage therapy, in which bacteriophages are administered as therapeutic antimicrobials. The smallest known tailed bacteriophages are the Salasmaviridae, Guelinviridae and Rountreeviridae, and represent families of bacterial viruses in the order Caudovirales (tailed dsDNA phages) characterised by their short linear DNA genomes The Salasmaviridae, Guelinviridae and Rountreeviridae phages are feasible candidates for phage engineering due to their small genome size, morphological resemblance, and the range of important human and animal pathogens they target (Bacillus, Clostridium, Staphylococcus, Streptococcus, Enterococcus). The GA1 phage of the Salasmaviridae family targets the pathogen Bacillus pumilus, causative of serious infant infections. The phiCPV4 phage belongs to the Guelinviridae family and infects Clostridium perfringens, a pathogenic scourge of the poultry industry, which causes foodborne illnesses in humans
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