PMID:9043137

Citation	Nieweg, A and Bremer, E (1997) The nucleoside-specific Tsx channel from the outer membrane of Salmonella typhimurium, Klebsiella pneumoniae and Enterobacter aerogenes: functional characterization and DNA sequence analysis of the tsx genes. Microbiology (Reading, Engl.) 143 ( Pt 2):603-15
Abstract	The Escherichia coli tsx gene encodes an integral outer-membrane protein (Tsx) that functions as a substrate-specific channel for deoxynucleosides and the antibiotic albicidin, and also serves as a receptor for bacteriophages and colicins. We cloned the structural genes of the Tsx proteins from Salmonella typhimurium, Klebsiella pneumoniae and Enterobacter aerogenes and expressed them in an E.coli tsx mutant. The heterologous Tsx proteins fully substituted the E.coli Tsx protein with respect to its function in deoxynucleoside and albicidin uptake, and as receptor for colicin K. The Tsx proteins from K. pneumoniae and Ent. aerogenes were also proficient as receptors for several Tsx-specific bacteriophages, whereas the corresponding protein from S. typhimurium did not confer sensitivity against these phages. The nucleotide sequence of the tsx genes from S. typhimurium, K. pneumoniae and Ent. aerogenes was established. Each of the Tsx proteins is initially synthesized with typical bacterial signal sequence peptides and the predicted mature forms of the Tsx proteins have a calculated M(r) of 30,567 (265 residues), 31,412 (272 residues) and 31,477 (272 residues), respectively. Multiple sequence alignments between the Tsx proteins showed a high degree of sequence identity and revealed the presence of four hypervariable regions, which are thought to constitute segments of the polypeptide chain exposed at the cell surface. Most notable was a deletion of 8 amino acids in one of these hypervariable domains in the S. typhimurium Tsx protein. When this deletion was introduced by site-directed mutagenesis into the corresponding region of the E.coli tsx gene, the mutant Tsx-515 protein lost its phage receptor function but still served as a colicin K receptor and as a substrate-specific channel, indicating that the region between residues 198 and 207 might be part of the bacteriophage receptor area. Multiple sequence alignments, structural predictions and the properties of previously characterized Tsx missense mutants were taken into account to develop a two-dimensional model for the topological organization of the Tsx protein within the outer membrane.
Links	PubMed
Keywords	Amino Acid Sequence; Bacterial Outer Membrane Proteins/genetics; Bacterial Outer Membrane Proteins/metabolism; Bacteriophages/metabolism; Base Sequence; Biological Transport/genetics; Cloning, Molecular; Colicins/metabolism; Enterobacter/genetics; Enterobacteriaceae/genetics; Escherichia coli/genetics; Escherichia coli Proteins; Genes, Bacterial; Ion Channels/genetics; Ion Channels/metabolism; Klebsiella pneumoniae/genetics; Molecular Sequence Data; Mutagenesis, Site-Directed; Nucleosides/metabolism; Protein Conformation; Receptors, Cell Surface/genetics; Receptors, Virus/genetics; Recombinant Proteins/metabolism; Salmonella typhimurium/genetics; Sequence Analysis, DNA; Sequence Homology, Amino Acid; Sequence Homology, Nucleic Acid
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
SALTY:TSX		GO:0016021: integral to membrane	ECO:0000315:		C		Fig. 3 The tsx gene product can be separated from the cell envelope proteins.	complete
SALTY:TSX		GO:0006810: transport	ECO:0000315:		P		Fig. 4. The expressed S.typhimurium Tsx proteins facilitated the efficient uptake of the deoxynucleoside and there was no strong difference in the initial rate compared to E. Coli Tsx. This protein functions as a substrate-specific channel.	complete
SALTY:TSX		GO:0022838: substrate-specific channel activity	ECO:0000315:		F		Fig. 4.& Table 2. The heterologous Tsx help to transport the deoxynucleoside. The strain with Tsx was fully sensitive to the antibiotic albicidin which depends on the Tsx channel for its permeation across the outer membrane. It functions as a substrate-specific channel.	complete

References

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