title: Using host-pathogen protein interactions to identify and characterize Francisella tularensis virulence factors.
abstract: BACKGROUND
  Francisella tularensis is a select bio-threat agent and one of the most virulent intracellular pathogens known, requiring just a few organisms to establish an infection. Although several virulence factors are known, we lack an understanding of virulence factors that act through host-pathogen protein interactions to promote infection. To address these issues in the highly infectious F. tularensis subsp. tularensis Schu S4 strain, we deployed a combined in silico, in vitro, and in vivo analysis to identify virulence factors and their interactions with host proteins to characterize bacterial infection mechanisms.
  
  
  RESULTS
  We initially used comparative genomics and literature to identify and select a set of 49 putative and known virulence factors for analysis. Each protein was then subjected to proteome-scale yeast two-hybrid (Y2H) screens with human and murine cDNA libraries to identify potential host-pathogen protein-protein interactions. Based on the bacterial protein interaction profile with both hosts, we selected seven novel putative virulence factors for mutant construction and animal validation experiments. We were able to create five transposon insertion mutants and used them in an intranasal BALB/c mouse challenge model to establish 50 % lethal dose estimates. Three of these, ΔFTT0482c, ΔFTT1538c, and ΔFTT1597, showed attenuation in lethality and can thus be considered novel F. tularensis virulence factors. The analysis of the accompanying Y2H data identified intracellular protein trafficking between the early endosome to the late endosome as an important component in virulence attenuation for these virulence factors. Furthermore, we also used the Y2H data to investigate host protein binding of two known virulence factors, showing that direct protein binding was a component in the modulation of the inflammatory response via activation of mitogen-activated protein kinases and in the oxidative stress response.
  
  
  CONCLUSIONS
  Direct interactions with specific host proteins and the ability to influence interactions among host proteins are important components for F. tularensis to avoid host-cell defense mechanisms and successfully establish an infection. Although direct host-pathogen protein-protein binding is only one aspect of Francisella virulence, it is a critical component in directly manipulating and interfering with cellular processes in the host cell.
authors.affiliation: Department of Defense Biotechnology High Performance Computing Software Applications Institute, Telemedicine and Advanced Technology Research Center, U.S. Army Medical Research and Materiel Command, Fort Detrick, MD, 21702, USA. awallqvist@bhsai.org.
authors.forename: Anders
authors.initials: A
authors.lastname: Wallqvist
authors.affiliation: Department of Defense Biotechnology High Performance Computing Software Applications Institute, Telemedicine and Advanced Technology Research Center, U.S. Army Medical Research and Materiel Command, Fort Detrick, MD, 21702, USA. vmemisevic@bhsai.org.
authors.forename: Vesna
authors.initials: V
authors.lastname: Memišević
authors.affiliation: Department of Defense Biotechnology High Performance Computing Software Applications Institute, Telemedicine and Advanced Technology Research Center, U.S. Army Medical Research and Materiel Command, Fort Detrick, MD, 21702, USA. nzavaljevski@bhsai.org.
authors.forename: Nela
authors.initials: N
authors.lastname: Zavaljevski
authors.affiliation: J. Craig Venter Institute, Rockville, MD, 20850, USA. rpieper@jcvi.org.
authors.forename: Rembert
authors.initials: R
authors.lastname: Pieper
authors.affiliation: J. Craig Venter Institute, Rockville, MD, 20850, USA. rvenkata@jcvi.org.
authors.forename: Seesandra V
authors.initials: SV
authors.lastname: Rajagopala
authors.affiliation: J. Craig Venter Institute, Rockville, MD, 20850, USA. kkwon@jcvi.org.
authors.forename: Keehwan
authors.initials: K
authors.lastname: Kwon
authors.affiliation: Department of Defense Biotechnology High Performance Computing Software Applications Institute, Telemedicine and Advanced Technology Research Center, U.S. Army Medical Research and Materiel Command, Fort Detrick, MD, 21702, USA. cyu@bhsai.org.
authors.forename: Chenggang
authors.initials: C
authors.lastname: Yu
authors.affiliation: Bacteriology Division, U.S. Army Medical Research Institute of Infectious Diseases, Fort Detrick, MD, 21702, USA. timothy.a.hoover14.civ@mail.mil.
authors.forename: Timothy A
authors.initials: TA
authors.lastname: Hoover
authors.affiliation: Department of Defense Biotechnology High Performance Computing Software Applications Institute, Telemedicine and Advanced Technology Research Center, U.S. Army Medical Research and Materiel Command, Fort Detrick, MD, 21702, USA. jaques.reifman.civ@mail.mil.
authors.forename: Jaques
authors.initials: J
authors.lastname: Reifman
mesh_terms: D000818:Animals; D005260:Female; D005604:Francisella tularensis / Q000235:genetics / Q000472:pathogenicity*; D054884:Host-Pathogen Interactions / Q000235:genetics*; D051379:Mice; D008807:Mice, Inbred BALB C; D011485:Protein Binding / Q000235:genetics / Q000502:physiology; D014774:Virulence / Q000235:genetics; D037521:Virulence Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: D037521:Virulence Factors