title: De Novo Guanine Biosynthesis but Not the Riboswitch-Regulated Purine Salvage Pathway Is Required for Staphylococcus aureus Infection In Vivo.
abstract: De novo guanine biosynthesis is an evolutionarily conserved pathway that creates sufficient nucleotides to support DNA replication, transcription, and translation. Bacteria can also salvage nutrients from the environment to supplement the de novo pathway, but the relative importance of either pathway during Staphylococcus aureus infection is not known. In S. aureus, genes important for both de novo and salvage pathways are regulated by a guanine riboswitch. Bacterial riboswitches have attracted attention as a novel class of antibacterial drug targets because they have high affinity for small molecules, are absent in humans, and regulate the expression of multiple genes, including those essential for cell viability. Genetic and biophysical methods confirm the existence of a bona fide guanine riboswitch upstream of an operon encoding xanthine phosphoribosyltransferase (xpt), xanthine permease (pbuX), inosine-5'-monophosphate dehydrogenase (guaB), and GMP synthetase (guaA) that represses the expression of these genes in response to guanine. We found that S. aureus guaB and guaA are also transcribed independently of riboswitch control by alternative promoter elements. Deletion of xpt-pbuX-guaB-guaA genes resulted in guanine auxotrophy, failure to grow in human serum, profound abnormalities in cell morphology, and avirulence in mouse infection models, whereas deletion of the purine salvage genes xpt-pbuX had none of these effects. Disruption of guaB or guaA recapitulates the xpt-pbuX-guaB-guaA deletion in vivo In total, the data demonstrate that targeting the guanine riboswitch alone is insufficient to treat S. aureus infections but that inhibition of guaA or guaB could have therapeutic utility.
  
  
  
  De novo guanine biosynthesis and purine salvage genes were reported to be regulated by a guanine riboswitch in Staphylococcus aureus We demonstrate here that this is not true, because alternative promoter elements that uncouple the de novo pathway from riboswitch regulation were identified. We found that in animal models of infection, the purine salvage pathway is insufficient for S. aureus survival in the absence of de novo guanine biosynthesis. These data suggest targeting the de novo guanine biosynthesis pathway may have therapeutic utility in the treatment of S. aureus infections.
authors.affiliation: Infectious Diseases Department, Genentech Inc., South San Francisco, California, USA kofoede@gene.com tan.man-wah@gene.com.
authors.forename: Eric M
authors.initials: EM
authors.lastname: Kofoed
authors.affiliation: Translational Immunology Department, Genentech Inc., South San Francisco, California, USA.
authors.forename: Donghong
authors.initials: D
authors.lastname: Yan
authors.affiliation: Pathology Department, Genentech Inc., South San Francisco, California, USA.
authors.forename: Anand K
authors.initials: AK
authors.lastname: Katakam
authors.affiliation: Pathology Department, Genentech Inc., South San Francisco, California, USA.
authors.forename: Mike
authors.initials: M
authors.lastname: Reichelt
authors.affiliation: Structural Biology Department, Genentech Inc., South San Francisco, California, USA.
authors.forename: Baiwei
authors.initials: B
authors.lastname: Lin
authors.affiliation: Translational Immunology Department, Genentech Inc., South San Francisco, California, USA.
authors.forename: Janice
authors.initials: J
authors.lastname: Kim
authors.affiliation: Translational Immunology Department, Genentech Inc., South San Francisco, California, USA.
authors.forename: Summer
authors.initials: S
authors.lastname: Park
authors.affiliation: Infectious Diseases Department, Genentech Inc., South San Francisco, California, USA.
authors.forename: Shailesh V
authors.initials: SV
authors.lastname: Date
authors.affiliation: Department of Microbiology and Immunology, University of Melbourne at the Doherty Institute for Infection and Immunity, Melbourne, Australia.
authors.forename: Ian R
authors.initials: IR
authors.lastname: Monk
authors.affiliation: Translational Immunology Department, Genentech Inc., South San Francisco, California, USA.
authors.forename: Min
authors.initials: M
authors.lastname: Xu
authors.affiliation: Pathology Department, Genentech Inc., South San Francisco, California, USA.
authors.forename: Cary D
authors.initials: CD
authors.lastname: Austin
authors.affiliation: Structural Biology Department, Genentech Inc., South San Francisco, California, USA.
authors.forename: Till
authors.initials: T
authors.lastname: Maurer
authors.affiliation: Infectious Diseases Department, Genentech Inc., South San Francisco, California, USA kofoede@gene.com tan.man-wah@gene.com.
authors.forename: Man-Wah
authors.initials: MW
authors.lastname: Tan
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D005260:Female; D015964:Gene Expression Regulation, Bacterial; D006147:Guanine / Q000096:biosynthesis*; D006801:Humans; D051379:Mice; D011687:Purines / Q000378:metabolism*; D058928:Riboswitch; D013203:Staphylococcal Infections / Q000382:microbiology*; D013211:Staphylococcus aureus / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D011687:Purines; D058928:Riboswitch; D006147:Guanine