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Proton-linked sugar transport systems in bacteria.
1Department of Biochemistry, University of Cambridge, United Kingdom.
Journal of Bioenergetics and Biomembranes
|August 1, 1990
Summary
Bacterial cell membranes utilize proton-linked transporters for various sugars. Gene sequencing reveals homologous transport proteins across diverse species, suggesting conserved structural and functional features for sugar uptake.
Area of Science:
- Molecular Biology
- Biochemistry
- Microbiology
Background:
- Cell membranes of bacteria and other organisms possess transport systems for various sugars, often linked to ion gradients.
- The melibiose transporter in E. coli exemplifies a system coupled to both sodium (Na+) and proton (H+) translocation.
- Understanding the specificity and structure of these sugar transporters is crucial for deciphering nutrient uptake mechanisms.
Purpose of the Study:
- To identify, clone, and sequence genes encoding sugar/H+ transporters in E. coli.
- To deduce the primary amino acid sequences of these transport proteins.
- To compare these sequences with known transporters from various organisms and predict common structural and functional motifs.
Main Methods:
- Gene identification, cloning, and sequencing of bacterial sugar/H+ transporters.
- Bioinformatic analysis of deduced amino acid sequences for homology and conserved regions.
- Comparison of bacterial transporter sequences with those from eukaryotes and other prokaryotes.
- Site-directed mutagenesis of E. coli lactose/H+ and melibiose/Na+(H+) transporters.
Main Results:
- Homology identified among E. coli xylose/H+, arabinose/H+, and galactose/H+ transporters, and with glucose transporters from diverse species (bacteria, yeast, algae, mammals).
- Predicted common structural features include twelve membrane-spanning alpha-helices and conserved amino acid motifs critical for substrate binding and transport.
- Mutagenesis studies pinpoint specific amino acid residues affecting sugar and cation recognition in E. coli transporters.
Conclusions:
- A conserved structural framework underlies sugar transport across a wide range of organisms, despite variations in cation coupling.
- Highly conserved amino acid residues likely play critical roles in the molecular mechanism of sugar transport.
- Further research can build upon these findings to elucidate the precise functions of identified transport proteins and their structural determinants.