Proline porters effect the utilization of proline as nutrient or osmoprotectant for bacteria

Abstract

Proline is utilized by all organisms as a protein constituent. It may also serve as a source of carbon, energy and nitrogen for growth or as an osmoprotectant. The molecular characteristics of the proline transport systems which mediate the multiple functions of proline in the Gram negative enteric bacteria, Escherichia coli and Salmonella typhimurium, are now becoming apparent. Recent research on those organisms has provided both protocols for the genetic and biochemical characterization of the enzymes mediating proline transport and molecular probes with which the degree of homology among the proline transport systems of archaebacteria, eubacteria and eukaryotes can be assessed. This review has provided a detailed summary of recent research on proline transport in E. coli and S. typhimurium; the properties of other organisms are cited primarily to illustrate the generality of those observations and to show where homologous proline transport systems might be expected to occur. The characteristics of proline transport in eukaryotic microorganisms have recently been reviewed (Horak, 1986).

Isolation, characterization, and expression of the Corynebacterium glutamicum betP gene, encoding the transport system for the compatible solute glycine betaine

“…A comparable domain was also found in ProP, the secondary transport system for glycine betaine and proline in E. coli (8). As shown for BetP, the ProP system is effectively regulated on the level of activity (14,32). It was suggested that the carboxy-terminal extension of ProP is associated with the ability to sense an osmoregulatory cellular signal (8).…”

Medium tonicity regulates expression of the Na(+)- and Cl(-)-dependent betaine transporter in Madin-Darby canine kidney cells by increasing transcription of the transporter gene.

“…Betaine is taken up by Escherichia coli and Salmonella typhimurium on transporters designated Pro P and Pro U, both identified originally as transport systems mediating uptake ofproline. Both systems have higher affinity for betaine than for proline, and the activity ofboth is increased in bacteria shifted to hypertonic media, the former increasing by > 10-fold, and the latter increasing > 100-fold (17). Transcription from the Pro U promoter has been reconstituted in vitro and shown to be stimulated by direct action of high concentrations of potassium glutamate (18), the major intracellular salt of bacteria.…”

Secondary solute transport in bacteria

“…More recently, it has been shown that the observed glutamate-H+-Na ÷ symport is the result of two activities (transport systems), i.e., GltS-mediated glutamate-Na ÷ symport [65] and GltP-mediated glutamate-H + symport [50]. A similar situation holds for proline transport in E. coli and S. typhimurium where the transport activities have been resolved to PutP-mediated proline-Na ÷ and ProPmediated proline-H ÷ symport activities [60,66,67]. The possibility that bacteria often possess more than one mechanism to transport a solute has to be taken into consideration when studies are performed under relatively undefined conditions, i.e., when purified proteins, defined host strains and/or cloned genes are not available.…”