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

• Published in: Genes Vol. 8; no. 12; p. 373
• Main Authors: Iverson, Eric A, Goodman, David A, Gorchels, Madeline E, Stedman, Kenneth M
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 08.12.2017; MDPI
• Subjects: Capsid protein; complementation; Deletion mutant; Gene deletion; Genes; Genetic analysis; Genomes; Infectivity; Insertion; morphology; mutants; Mutation; N-Terminus; Protein structure; Proteins; Proteolysis; Site-directed mutagenesis; Virions; Viruses; VP1 protein; VP3 protein; site-directed mutagenesis; morphology; complementation; mutants; proteolysis
• ISSN: 2073-4425; 2073-4425
• DOI: 10.3390/genes8120373

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, Sulfolobus Spindle-shaped Virus 1 (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 gene , the gene does not tolerate deletion or transposon insertion. To determine the role of the gene and its proteolysis for virus function, we developed techniques for site-directed mutagenesis of the SSV1 genome and complemented deletion mutants with 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 for infectivity. Interestingly, viruses containing point mutations at this position generate mostly abnormal virions.