Abstract
The mature virion of the tailed bacteriophage ϕ29 is an ~33 MDa complex that contains more than 450 subunits of seven structural proteins assembling into a prolate head and a short non-contractile tail. Here, we report the near-atomic structures of the ϕ29 pre-genome packaging head (prohead), the mature virion and the genome-emptied virion. Structural comparisons suggest local rotation or oscillation of the head-tail connector upon DNA packaging and release. Termination of the DNA packaging occurs through pressure-dependent correlative positional and conformational changes in the connector. The funnel-shaped tail lower collar attaches the expanded narrow end of the connector and has a 180-Å long, 24-strand β barrel narrow stem tube that undergoes conformational changes upon genome release. The appendages form an interlocked assembly attaching the tail around the collar. The membrane active long loops at the distal end of the tail knob exit during the late stage of infection and form the cone-shaped tip of a largely hydrophobic helix barrel, prepared for membrane penetration.
Highlights
The mature virion of the tailed bacteriophage φ29 is an ~33 MDa complex that contains more than 450 subunits of seven structural proteins assembling into a prolate head and a short non-contractile tail
Our results showed that the 448-amino-acid-long polypeptide chain of the major capsid protein gp[8] folds into three structural domains: the small N-terminal helix domain, the central HK97 fold domain and the C-terminal immunoglobulin-like domain (Fig. 2a and Supplementary Fig. 3a)
The structure of the central HK97 domain closely resembles that of the HK97 capsid protein, which has two subdomains with extensions (N-arm and E-loop) (Fig. 2a)
Summary
The mature virion of the tailed bacteriophage φ29 is an ~33 MDa complex that contains more than 450 subunits of seven structural proteins assembling into a prolate head and a short non-contractile tail. Φ29 infects the Gram-positive Bacillus subtilis cells by injecting the genome–gp[3] complex into the host-cell cytoplasm using a short non-contractile tail, leaving the genome emptied virion on the cell surface (Fig. 1a). A dsDNA packaging machinery is assembled on the prohead by attaching a viral encoded short prohead RNA (pRNA) and the ATPase gp[16] around the connector[7,8,9]. Previous low-resolution electron microscopy (EM) structural studies showed that the major capsid proteins of the mature φ29 head assemble to form a T = 3, Q = 5 prolate icosahedron[2,15,16,17]
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