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Keywords = prohead protease

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17 pages, 4462 KB  
Article
Mass Spectral Analyses of Salmonella Myovirus SPN3US Reveal Conserved and Divergent Themes in Proteolytic Maturation of Large Icosahedral Capsids
by Aaron Scheuch, Sara A. M. Moran, Julia N. Faraone, Sophia R. Unwin, Gialinh Vu, Andrea Denisse Benítez, Nurul Humaira Mohd Redzuan, Dana Molleur, Sammy Pardo, Susan T. Weintraub and Julie A. Thomas
Viruses 2023, 15(3), 723; https://doi.org/10.3390/v15030723 - 10 Mar 2023
Cited by 1 | Viewed by 2949
Abstract
Salmonella myovirus SPN3US has a T = 27 capsid composed of >50 different gene products, including many that are packaged along with the 240 kb genome and ejected into the host cell. Recently, we showed that an essential phage-encoded prohead protease gp245 is [...] Read more.
Salmonella myovirus SPN3US has a T = 27 capsid composed of >50 different gene products, including many that are packaged along with the 240 kb genome and ejected into the host cell. Recently, we showed that an essential phage-encoded prohead protease gp245 is responsible for cleavage of proteins during SPN3US head assembly. This proteolytic maturation step induces major changes in precursor head particles, enabling them to expand and undergo genome packaging. To comprehensively define the composition of the mature SPN3US head and elucidate how it is modified by proteolysis during assembly, we conducted tandem mass spectrometry analysis of purified virions and tailless heads. Fourteen protease cleavage sites were identified in nine proteins, including eight sites not previously identified in head proteins in vivo. Among these was the maturation cleavage site of gp245 which was identical to the autocleavage site we had previously identified in purified recombinant gp245. Our findings underscore the value of employing multiple mass spectrometry-based experimental strategies as a way to enhance the detection of head protein cleavage sites in tailed phages. In addition, our results have identified a conserved set of head proteins in related giant phages that are similarly cleaved by their respective prohead proteases, suggesting that these proteins have important roles in governing the formation and function of large icosahedral capsids. Full article
(This article belongs to the Special Issue Viral Proteases: Modulation of Immune Responses and Antiviral Therapies)
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22 pages, 9876 KB  
Article
A Cut above the Rest: Characterization of the Assembly of a Large Viral Icosahedral Capsid
by Erin R. Reilly, Milky K. Abajorga, Cory Kiser, Nurul Humaira Mohd Redzuan, Zein Haidar, Lily E. Adams, Randy Diaz, Juliana A. Pinzon, André O. Hudson, Lindsay W. Black, Ru-Ching Hsia, Susan T. Weintraub and Julie A. Thomas
Viruses 2020, 12(7), 725; https://doi.org/10.3390/v12070725 - 5 Jul 2020
Cited by 11 | Viewed by 5153
Abstract
The head of Salmonella virus SPN3US is composed of ~50 different proteins and is unusual because within its packaged genome there is a mass (>40 MDa) of ejection or E proteins that enter the Salmonella cell. The assembly mechanisms of this complex structure [...] Read more.
The head of Salmonella virus SPN3US is composed of ~50 different proteins and is unusual because within its packaged genome there is a mass (>40 MDa) of ejection or E proteins that enter the Salmonella cell. The assembly mechanisms of this complex structure are poorly understood. Previous studies showed that eight proteins in the mature SPN3US head had been cleaved by the prohead protease. In this study, we present the characterization of SPN3US prohead protease mutants using transmission electron microscopy and mass spectrometry. In the absence of the prohead protease, SPN3US head formation was severely impeded and proheads accumulated on the Salmonella inner membrane. This impediment is indicative of proteolysis being necessary for the release and subsequent DNA packaging of proheads in the wild-type phage. Proteomic analyses of gp245- proheads that the normal proteolytic processing of head proteins had not occurred. Assays of a recombinant, truncated form of the protease found it was active, leading us to hypothesize that the C-terminal propeptide has a role in targeting the protease into the prohead core. Our findings provide new evidence regarding the essential role of proteolysis for correct head assembly in this remarkable parasite. Full article
(This article belongs to the Special Issue Giant or Jumbo Phages)
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