Abstract
Archaeal viruses have evolved to infect hosts often thriving in extreme conditions such as high temperatures. However, there is a paucity of information on archaeal virion structures, genome packaging, and determinants of temperature resistance. The rod-shaped virus APBV1 (Aeropyrum pernix bacilliform virus 1) is among the most thermostable viruses known; it infects a hyperthermophile Aeropyrum pernix, which grows optimally at 90 °C. Here we report the structure of APBV1, determined by cryo-electron microscopy at near-atomic resolution. Tight packing of the major virion glycoprotein (VP1) is ensured by extended hydrophobic interfaces, and likely contributes to the extreme thermostability of the helical capsid. The double-stranded DNA is tightly packed in the capsid as a left-handed superhelix and held in place by the interactions with positively charged residues of VP1. The assembly is closed by specific capping structures at either end, which we propose to play a role in DNA packing and delivery.
Highlights
Archaeal viruses have evolved to infect hosts often thriving in extreme conditions such as high temperatures
The unusual morphotypes of hyperthermophilic archaeal viruses appear to be determined by exceptional ways of genome packaging and virion morphogenesis, which apparently secure the stability of virions in extreme conditions of the natural environments[1]
To study the molecular basis of the extreme temperature resistance of APBV1, we have determined the three-dimensional structure of the purified APBV1 virion using electron cryomicroscopy to ~3-Å resolution
Summary
Archaeal viruses have evolved to infect hosts often thriving in extreme conditions such as high temperatures. Virion structures of the icosahedral virus STIV and the filamentous viruses SIRV2 and AFV1 of the hyperthermophilic archaeal order Sulfolobales have been described at high resolution[3,4,5]. The double-stranded, circular DNA genome of the virus (5.3 kbp) is among the smallest known dsDNA genomes[7] It encodes for the major capsid protein (MCP) VP1 (8.3 kDa) in addition to three minor capsid proteins VP2 (9.7 kDa), VP3 (11.2 kDa), and VP4 (21.4 kDa). To study the molecular basis of the extreme temperature resistance of APBV1, we have determined the three-dimensional structure of the purified APBV1 virion using electron cryomicroscopy (cryo-EM) to ~3-Å resolution. The inner surface of the tube is positively charged to allow efficient interactions with the circular dsDNA genome Together, these interactions stabilize the virus particle. The structure allows us to propose an assembly model where the dsDNA genome and capsid assemble in a concerted fashion
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