How Hemorrhagic E. coli pH Sensitivity of the Glu-GABA Antiporter aibdor 300- Resists the Acid Environment pnit of the Stomach GadC AdiC 250 TEE 200/l ilorlqgori A dmM a 2nieto19 bbbed Recent years have been marked by a series of food poisoning outbreaks involving hemorrhagic (producingA internal bleeding) strains of the bacterium Escherichia coli (E. coli), Bacteria are often a source of food poisoning,.e 150 dii velid biqilodqzorlq to 219orda An oilidoovd brs bucwni b5lngho anoigo1idod oi2nio .lobom oinzom ort nl buwino b oitoM typically milder infections caused by food-borne strepto-nol 100 coccal bacteria. Less able to bear the extremely acidic conditions encountered by food in the human stomach problem. The hemorrhagic strains of E. coli responsible for recent out- 0yelid bin o 50 u r bo dmea mnslslulle OTOT SLTT DITBIO 21901071A ns c2nrotong smsidmomang 1Vlid biqilorlqeodq onogmos 1o1ni orT uz-lleo bnsTOWen nistogongus bne eihotwhr ibIolewooiyoio bodoqunoo C1 AOw bpiog ordi riiw botsioozz w.zniotonq onEidmom Isdgoog no abiqiloovig bns anioiongoomistmoo 2snsidmsMonsdaoon 2), E. coli has not been as common a (pH = 8 7 6 breaks seem to have evolved more elaborate acid-resistance lid biqilordgeodg 5 ww.toqad pH systems. usionrod! miaulib How do hemorrhagic E. coli bacteria survive in the PALD 1O DHUo acid environment of the stomach? The problem they o 10 face, in essence, is that they are submerged in a sea of hydrogenr .21acamansbi lloo 2s o tsd) soriggeort ions, many of which diffuse into their cells. To rid them-nnt Analysis selves of these excess hydrogen ions, the E. coli cells use aom Applying Concepts vo19 abiqilorlqeorl9 aRE a. Variable. In the graph, what is the dependent o l6ulpu/2 clever system to pump hydrogen ions back out of their EA.a cells. p.opp9ub,orlT espeadmeM First, the hemorrhagic E. coli cells take up cellulari no b. Substrate. What is a substrate? In thislia biqil erlT investigation, what are the substrates that 20 o.cns accumulatingon lognon.16 20r3 c. pH. What is the difference in hydrogen ion concentration between pH 5 and pH 7? 1ootni o oonm How many times more (or less) is that? Explain.w b om 2. Interpreting Data mords 2qs lo gmibnod nogoib hhopom a. Does the amount of amino acid transported in the 10-minute experimental interval (expressed as substrate accumulation) vary with pH for the arginine-transporting AdiC b antiporter? For the glutamate-transportinginooi GadC antiporter? b. Compare the amount of substrate accumulated by AdiC in 10 minutes at pH 9.0 with that accumulated at pH 5.0. What fraction of the low pH activity is observed at the higher pH c. In a similar fashion, compare the amount of substrate accumulated by GadC at pH 9.0 with that accumulated at pH 5.0. What fraction of the low pH activity is observed at the higher pH? 3. Making Inferences Would you say that the GadC antiporter exhibits the same AdiC antiporter? If not, which antiporter is less active at nonacid pHs? 4. Drawing Conclusions Is the glutamate-GABA antiporter GadC active at nonacid pHs? e.u variable? 1eMirsoHPo hydrogen ions by using the enzyme glutamic acid decarbox- ylase (GAD) to convert the amino acid glutamate to Y-aminobutyric acid (GABA), a decarboxylation reaction that uloc omeo 00 nOituloz inOI0RI nlo ig20r0 are OTSOvi nodusoco.om Y pdspailidqono.bm WS 3ner1o yURG OIBE O20 stods loa ns rY.i: consumes a hydrogen ion. Second, the hemorrhagic E. coli export this GABA 6W S2O from their cell cytoplasm using a Glu-GABA antiporter called GadC (this transmembrane protein channel is called an antiporter because it transports two molecules across the membrane in opposite directions). GO 2 However, to survive elsewhere in the human body, itex is important that the Glu-GABA antiporter of hemorrhagic aa E. coli not function, lest it short-circuit metabolism. To see if the GadC antiporter indeed functions only in acid environ-o to ments, investigators compared its activity at a variety of pHsono with that of a different amino acid antiporter called AdiC, which transports arginine out of cells under a broad range of conditions. The results of monitoring transport for loo nt to sam dmsM 9TA 20118 10 minutes are presented in the graph. natbena nbibenb no Aydhoatiysnone oru Joganett belquo ce neono iedT tenisgA eoluseloM w.ewppo 0ansit My0fhoa roibeTg uoginm Ispsdst Outside oloonb Inside cell tbeib.sh20g notasdbo lleo-01-115O cell : en pH dependence as the dmeMacor2aghelah GABA neit aT 2bi ebloA one aleoiyacbte Ne boa el 5. Further Analysis The GadC antiporter also Glutamate pondl transports the amino acid glutamine (Gln). Do you think this activity has any role to play in combating low pH environments? How would you test this hypothesis? Substrate accumulation (nmol per mg protein) Inquiry & Analysis