title: Requirements for osmosensing and osmotic activation of transporter ProP from Escherichia coli.
abstract: Transporter ProP of Escherichia coli, a solute-H+ symporter, can sense and respond to osmotic upshifts imposed on cells, on membrane vesicles, or on proteoliposomes that incorporate purified ProP-(His)6. In this study, proline uptake catalyzed by ProP was used as a measure of its osmotic activation, and the requirements for osmosensing were defined using the proteoliposome system. The initial rate of proline uptake increased with decreasing external pH and increasing DeltaPsi, lumen negative. Osmotic upshifts increased DeltaPsi by concentrating lumenal K+, but osmotic activation of ProP could be distinguished from this effect. Osmotic activation of ProP resulted from changes in Vmax, though osmotic shifts also increased the KM for proline. Osmotic activation could be described as a reversible, osmotic upshift-dependent transition linking (at least) two transporter protein conformations. No correlation was observed between ProP activation and the position of the anions of activating sodium salts within the Hofmeister series of solutes. Both the magnitude of the osmotic upshift required to activate ProP and the ProP activity attained were similar for membrane-impermeant osmolytes, including NaCl, glucose, and PEG 600. The membrane-permeant osmolytes glycerol, urea, PEG 62, and PEG 106 failed to activate ProP. Two poly(ethylene glycol)s, PEG 150 and PEG 200, were membrane-permeant and did not cause liposome shrinkage, but they did partially activate ProP-(His)6.
authors.affiliation: Department of Microbiology and Guelph-Waterloo Centre for Graduate Work in Chemistry and Biochemistry, University of Guelph, Guelph, Ontario N1G 2W1, Canada.
authors.forename: K I
authors.initials: KI
authors.lastname: Racher
authors.forename: D E
authors.initials: DE
authors.lastname: Culham
authors.forename: J M
authors.initials: JM
authors.lastname: Wood
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D029968:Escherichia coli Proteins; D005960:Glucosides / Q000494:pharmacology; D006639:Histidine / Q000235:genetics; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008081:Liposomes / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects / Q000235:genetics; D009994:Osmolar Concentration; D009997:Osmotic Pressure / Q000187:drug effects; D010957:Plasmids / Q000378:metabolism; D011092:Polyethylene Glycols / Q000494:pharmacology; D011510:Proteolipids / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D012965:Sodium Chloride / Q000494:pharmacology; D012996:Solutions; D027981:Symporters
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; D005960:Glucosides; D008081:Liposomes; C079244:ProP protein, E coli; D011510:Proteolipids; D012996:Solutions; D027981:Symporters; C109438:di-(glucos-6-yl)-PEG(600); C020485:proteoliposomes; D011092:Polyethylene Glycols; D012965:Sodium Chloride; D006639:Histidine