Osmostress response in Bacillus subtilis: characterization of a proline uptake system (OpuE) regulated by high osmolarity and the alternative transcription factor sigma B
Abstract
Exogenously provided proline has been shown to serve as an osmoprotectant in Bacillus subtilis. Uptake of proline is under osmotic control and functions independently of the known transport systems for the osmoprotectant glycine betaine. We cloned the structural gene (opuE) for this proline transport system and constructed a chromosomal opuE mutant by marker replacement. The resulting B. subtilis strain was entirely deficient in osmoregulated proline transport activity and was no longer protected by exogenously provided proline, attesting to the central importance of OpuE for proline uptake in high-osmolarity environments. The transport characteristics and growth properties of the opuE mutant revealed the presence of a second proline transport activity in B. subtilis. DNA sequence analysis of the opuE region showed that the OpuE transporter (492 residues) consists of a single integral membrane protein. Database searches indicated that OpuE is a member of the sodium/solute symporter family, comprising proteins from both prokaryotes and eukaryotes that obligatorily couple substrate uptake to Na+ symport. The highest similarity was detected to the PutP proline permeases, which are used in Escherichia coli, Salmonella typhimurium a...Continue Reading
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