Sugar transport through maltoporin of Escherichia coli : role of the greasy slide

Van Gelder, Patrick and Dumas, Fabrice and Bartoldus, Ingrid and Saint, Nathalie and Prilipov, Alexei and Winterhalter, Mathias and Wang, Yanfei and Philippsen, Ansgar and Rosenbusch, Jürg P. and Schirmer, Tilman. (2002) Sugar transport through maltoporin of Escherichia coli : role of the greasy slide. Journal of Bacteriology, 184 (11). pp. 2994-2999.

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The lining of the maltodextrin-specific maltoporin (LamB) channel exhibits a string of aromatic residues, the greasy slide, part of which has been shown previously by crystallography to be involved in substrate binding. To probe the functional role of the greasy slide, alanine scanning mutagenesis has been performed on the six greasy slide residues and Y118 at the channel constriction. The mutants were characterized by an in vivo uptake assay and sugar-induced-current-noise analysis. Crystallographic analysis of the W74A mutant showed no perturbation of the structure. All mutants showed considerably decreased maltose uptake rates in vivo (>10% of the wild-type value), indicating the functional importance of the investigated residues. Substitutions at the channel center revealed appreciably increased (up to 100-fold) in vitro half-saturation concentrations for maltotriose and maltohexaose binding to the channel. Sugar association rates, however, were significantly affected also by the mutations at either end of the slide (W74A, W358A, and F227A), an effect which became most apparent upon nonsymmetrical sugar addition. The kinetic data are discussed on the basis of an asymmetric one-site two-barrier model, which suggests that, at low substrate concentrations, as are found under physiological conditions, only the heights of the extracellular and periplasmic barriers, which are reduced by the presence of the greasy slide, determine the efficiency of this facilitated diffusion channel.
Faculties and Departments:05 Faculty of Science > Departement Biozentrum > Former Organization Units Biozentrum > Structural Biology (Schirmer)
UniBasel Contributors:Schirmer, Tilman
Item Type:Article, refereed
Article Subtype:Research Article
Publisher:American Society for Microbiology
Note:Publication type according to Uni Basel Research Database: Journal article
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Last Modified:10 Aug 2018 13:59
Deposited On:22 Mar 2012 13:20

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