Přehled o publikaci

Staphylococcus aureus phage phi812 is a promising agent for phage therapy due to its lytic activity against a broad host range, including antibiotic antibiotic-resistant and biofilm biofilm-forming strains. To fill the gaps in knowledge about phi812 head assembly, this work used cryo-electron tomography (cryo-ET) and cryo-electron microscopy (cryo-EM). Cryo-ET data revealed sequential stages of head assembly in infected cells: membrane membrane-associated cup cup-like precursors, spherical proheads I, expanded proheads II, and DNA-filled mature heads. Sub-tomogram averaging revealed three distinct structures of phage assembly intermediates, differing in size and surface features. These include prohead I, genome-packaging intermediate of prohead II, and the DNA-filled head, with resolutions of 35, 45, and 31 Å, respectively. The icosahedral reconstruction of phi812 head assembly intermediates resulted in three prohead II classes that differ in the occupancy of minor capsid proteins. The mature head and prohead II display a similar overall organization of the major capsid proteins. During DNA packaging, the asymmetric unit of prohead II undergoes an inward tilt of ~1.6° around a pivot point at the 5 5-fold axes, leading to capsid flattening and a slight size contraction in the mature head. This study provides detailed structural insight into the in situ assembly of phage phi812 heads in S. aureus. Cryo-ET captured key stages of head maturation. High-resolution cryo-EM revealed that maturation involves radial expansion, followed by compaction and stepwise incorporation of minor capsid proteins.