title: DsdX is the second D-serine transporter in uropathogenic Escherichia coli clinical isolate CFT073.
abstract: d-Serine is an amino acid present in mammalian urine that is inhibitory to Escherichia coli strains lacking a functional dsdA gene. Counterintuitively, a dsdA strain of E. coli clinical isolate CFT073 hypercolonizes the bladder and kidneys of mice relative to wild type during a coinfection in the murine model of urinary tract infection. We are interested in the mechanisms for uptake of d-serine in CFT073. d-Serine enters E. coli K-12 via CycA, the d-alanine transporter and d-cycloserine sensitivity locus. CFT073 cycA can grow on minimal medium with d-serine as a sole carbon source. The dsdX gene of the dsdCXA locus is a likely candidate for an additional d-serine transporter based on its predicted amino acid sequence similarity to gluconate transporters. In minimal medium, CFT073 dsdX can grow on d-serine as a sole carbon source; however, CFT073 dsdX cycA cannot. Additionally, CFT073 dsdXA cycA is not sensitive to inhibitory concentrations of d-serine during growth on glycerol and d-serine minimal medium. d-[(14)C]serine uptake experiments with CFT073 dsdX cycA harboring dsdX or cycA recombinant plasmids confirm that d-serine is able to enter E. coli cells via CycA or DsdX. In whole-cell d-[(14)C]serine uptake experiments, DsdX has an apparent K(m) of 58.75 microM and a V(max) of 75.96 nmol/min/mg, and CycA has an apparent K(m) of 82.40 microM and a V(max) of 58.90 nmol/min/mg. Only d-threonine marginally inhibits DsdX-mediated d-serine transport, whereas d-alanine, glycine, and d-cycloserine inhibit CycA-mediated d-serine transport. DsdX or CycA is sufficient to transport physiological quantities of d-serine, but DsdX is a d-serine-specific permease.
authors.affiliation: Department of Medical Microbiology & Immunology, University of Wisconsin-Madison, 1300 University Ave., Room 481 MSC, Madison, WI 53706, USA.
authors.forename: Andrew T
authors.initials: AT
authors.lastname: Anfora
authors.forename: Rodney A
authors.initials: RA
authors.lastname: Welch
mesh_terms: D000409:Alanine / Q000378:metabolism; D026905:Amino Acid Transport Systems / Q000235:genetics / Q000502:physiology; D001692:Biological Transport / Q000235:genetics; D003470:Culture Media / Q000737:chemistry; D003523:Cycloserine / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism* / Q000472:pathogenicity; D029968:Escherichia coli Proteins / Q000235:genetics / Q000502:physiology*; D017353:Gene Deletion; D005998:Glycine / Q000378:metabolism; D007700:Kinetics; D026901:Membrane Transport Proteins / Q000235:genetics / Q000502:physiology*; D008954:Models, Biological; D012694:Serine / Q000378:metabolism*; D013912:Threonine / Q000378:metabolism
chemical_list: D026905:Amino Acid Transport Systems; D003470:Culture Media; C510329:CycA protein, E coli; C096748:DsdX protein, E coli; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D013912:Threonine; D012694:Serine; D003523:Cycloserine; D000409:Alanine; D005998:Glycine