The ion coupling and organic substrate specificities of osmoregulatory transporter ProP in Escherichia coli

• Published in: Biochimica et biophysica acta Vol. 1420; no. 1; pp. 30 - 44
• Main Authors: MacMillan, Susan V., Alexander, David A., Culham, Doreen E., Kunte, H.Jörg, Marshall, Emmalee V., Rochon, Denis, Wood, Janet M.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 20.08.1999
• Subjects: Bacterial Proteins - antagonists & inhibitors; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Betaine - metabolism; Biological Transport, Active; Carrier Proteins - antagonists & inhibitors; Carrier Proteins - genetics; Carrier Proteins - metabolism; Choline - metabolism; Choline - pharmacology; Escherichia coli; Escherichia coli - genetics; Escherichia coli - metabolism; Escherichia coli Proteins; Hydrogen-Ion Concentration; Ion Transport; Kinetics; Osmoregulation; Potassium - metabolism; Proline - metabolism; Proton symport; Substrate specificity; Symporters; Transporter ProP; Water-Electrolyte Balance; Osmoregulation; Transporter ProP; Escherichia coli; Substrate specificity; Proton symport
• ISSN: 0005-2736; 0006-3002; 1879-2642; 1878-2434
• DOI: 10.1016/S0005-2736(99)00085-1

Transporter ProP of Escherichia coli, a member of the major facilitator superfamily, mediates osmoprotective proline or glycine betaine accumulation by bacteria exposed to high osmolality environments. Morpholinopropane sulfonic acid, a common constituent of microbiological media, accumulates in osmoadapting E. coli cells but it is not osmoprotective and it did not influence proP transcription or ProP activity. The apparent K m for proline uptake via ProP increased with decreasing pH in the range 7.5–4. ProP-dependent proline uptake by de-energized bacteria was associated with alkalinization of the external medium. Thus ProP mediates cotransport of H + and zwitterionic proline and a transporter functional group with a p K a of 5–6 is implicated in catalysis. Exogenous proline or glycine betaine elicits K + release from osmoadapting E. coli cells and ProP activity is stimulated by exogenous K +. However, uptake of proline or glycine betaine stimulated K + efflux from K +-loaded bacteria which expressed either ProP or alternative, osmoregulatory transporter ProU. This indicated that ProP was unlikely to mediate K + efflux. Zwitterions ectoine, pipecolate, proline betaine, N, N-dimethylglycine, carnitine and 1-carboxymethylpyridinium were identified as alternative ProP substrates. Choline, a cation and a structural analogue of glycine betaine, was a low affinity inhibitor but not a substrate of ProP.