title: Evolution of an archaeal virus nucleocapsid protein from the CRISPR-associated Cas4 nuclease.
abstract: Many proteins of viruses infecting hyperthermophilic Crenarchaeota have no detectable homologs in current databases, hampering our understanding of viral evolution. We used sensitive database search methods and structural modeling to show that a nucleocapsid protein (TP1) of Thermoproteus tenax virus 1 (TTV1) is a derivative of the Cas4 nuclease, a component of the CRISPR-Cas adaptive immunity system that is encoded also by several archaeal viruses. In TTV1, the Cas4 gene was split into two, with the N-terminal portion becoming TP1, and lost some of the catalytic amino acid residues, apparently resulting in the inactivation of the nuclease. To our knowledge, this is the first described case of exaptation of an enzyme for a virus capsid protein function.
authors.affiliation: Department of Microbiology, Unité Biologie Moléculaire du Gène chez les Extrêmophiles, Institut Pasteur, Paris, 75015, France. krupovic@pasteur.fr.
authors.forename: Mart
authors.initials: M
authors.lastname: Krupovic
authors.affiliation: Department of Microbiology, Unité Biologie Moléculaire du Gène chez les Extrêmophiles, Institut Pasteur, Paris, 75015, France. virginija.cvirkaite-krupovic@pasteur.fr.
authors.forename: Virginija
authors.initials: V
authors.lastname: Cvirkaite-Krupovic
authors.affiliation: Department of Microbiology, Unité Biologie Moléculaire du Gène chez les Extrêmophiles, Institut Pasteur, Paris, 75015, France. david.prangishvili@pasteur.fr.
authors.forename: David
authors.initials: D
authors.lastname: Prangishvili
authors.affiliation: National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD, 20894, USA. koonin@ncbi.nlm.nih.gov.
authors.forename: Eugene V
authors.initials: EV
authors.lastname: Koonin
mesh_terms: D019843:Archaeal Proteins / Q000235:genetics* / Q000378:metabolism; D064113:CRISPR-Cas Systems; D004720:Endonucleases / Q000235:genetics* / Q000378:metabolism; D019143:Evolution, Molecular; D023643:Lipothrixviridae / Q000201:enzymology* / Q000235:genetics*; D019590:Nucleocapsid Proteins / Q000235:genetics* / Q000378:metabolism; D041542:Thermoproteus / Q000235:genetics / Q000821:virology
chemical_list: D019843:Archaeal Proteins; D019590:Nucleocapsid Proteins; D004720:Endonucleases