The C-4 hydroxyl group of galactopyranosides is the major determinant for ligand recognition by the lactose permease of Escherichia coli
| Autor: | H R Kaback, M C Lawrence, Miklós Sahin-Tóth, Nishio T |
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| Rok vydání: | 2001 |
| Předmět: |
Lactose permease
Monosaccharide Transport Proteins Stereochemistry Carbohydrates Alkylation Ligands Biochemistry Hydrophobic effect Escherichia coli Moiety Binding site Amino Acids Binding selectivity Binding Sites Dose-Response Relationship Drug Symporters Chemistry Escherichia coli Proteins Cell Membrane Substrate (chemistry) Galactose Membrane Transport Proteins Ligand (biochemistry) Kinetics Models Chemical Protein Binding |
| Zdroj: | Biochemistry. 40(43) |
| ISSN: | 0006-2960 |
| Popis: | Binding specificity in lactose permease toward galactopyranosides is governed by H-bonding interactions at C-2, C-3, C-4, and C-6 OH groups, while binding affinity can be increased dramatically by nonspecific hydrophobic interactions with the non-galactosyl moiety [Sahin-Toth, M., Akhoon, K. M., Runner, J., and Kaback, H. R. (2000) Biochemistry 39, 5097-5103]. To characterize the contribution of individual hydroxyls, binding of structural analogues of p-nitrophenyl alpha-D-galactopyranoside (NPG) was examined by site-directed N-[(14)C]ethylmaleimide (NEM) labeling of the substrate-protectable Cys148 in the binding site. NPG blocks NEM alkylation of Cys148 with an apparent affinity of approximately 14 microM. A deoxy derivative at position C-2 binds with 25-fold lower affinity (K(D) 0.35 mM), and the deoxy analogue at C-3 exhibits ca. 70-fold decreased binding (K(D) 1 mM), while binding of 6-deoxy-NPG is at least 130-fold diminished (K(D) 1.9 mM). Remarkably, the C-4 deoxy derivative of NPG binds with almost 1500-fold reduced affinity (K(D) approximately 20 mM). No significant substrate protection is afforded by NPG analogues with methoxy (CH(3)-O-) substitutions at positions C-3, C-4, and C-6. In contrast, the C-2 methoxy analogue binds almost normally (K(D) 26 microM). The results confirm and extend the observations that the C-2, C-3, C-4, and C-6 OH groups of galactopyranosides participate in important H-bonding interactions. Moreover, the C-4 hydroxyl is identified as the major determinant of ligand binding, suggesting that sugar recognition in lactose permease may have evolved to discriminate primarily between gluco- and galactopyranosides. |
| Databáze: | OpenAIRE |
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