Genetic Analysis of the Major Capsid Protein of the Archaeal Fusellovirus SSV1: Mutational Flexibility and Conformational Change

Abstract

Abstract:Viruses with spindle or lemon-shaped virions are rare in the world of viruses, but are common in viruses of archaeal extremophiles, possibly due to the extreme conditions in which they thrive. However, the structural and genetic basis for the unique spindle shape is unknown. The best-studied spindle-shaped virus, SSV1, is composed mostly of the major capsid protein VP1. Similar to many other viruses, proteolytic cleavage of VP1 is thought to be critical for virion formation.Unlike half of the genes in SSV1, including the minor capsid protein VP3, the vp1 gene does not tolerate deletion or transposon insertion. In order determine the role of the vp1 gene and its proteolysis for virus function, we developed techniques for site-directed mutagenesis of the SSV1 genome and complemented deletion mutants with vp1 genes from other SSVs. By analyzing these mutants we demonstrate that the N-terminus of the VP1 protein is required, but the N-terminus, or entire SSV1 VP1 protein, can be exchanged with VP1s from other SSVs. However, the conserved glutamate at the cleavage site is not essential. Interestingly, viruses containing point mutations at this position generate mostly abnormal virions.

Comparative genetic and genomic analysis of the novel fusellovirus Sulfolobus spindle-shaped virus 10

“…2012 ) and is susceptible to infection by multiple wild-type SSVs as well as an array of SSV1 deletion and insertion mutants ( Iverson et al. 2017a , b ). All Sulfolobus strains, both infected and uninfected, were isolated as in Zillig et al.…”

“…Deletions of SSV10 ORFs were made using long-inverse polymerase chain reaction (LIPCR) as described previously ( Clore and Stedman 2007 ; Iverson and Stedman 2012 ; Iverson et al. 2017a , b ). The T m calculator software ( http://tmcalculator.neb.com/# !/ ) was used to estimate the annealing temperatures for each primer pair ( Supplementary Table S1 ).…”

Structure and assembly of archaeal viruses

“…Notably, prior to virion assembly, VP1 is proteolytically processed by an unidentified protease at a conserved glutamate residue, removing the N-terminal region (Quemin et al, 2015;Reiter et al, 1987). However, the gene fragment encoding this region could not be deleted (Iverson et al, 2017b), suggesting that it is important for correct subcellular protein localization and/or virion morphogenesis. Subsequently, the neck of the budding virus particle is constricted at the base, sealing the host membrane and releasing the virion (Fig.…”