Structural insights into the activation mechanism of melibiose permease by sodium binding

Meritxell Granell, Xavier León, Gérard Leblanc, Esteve Padrós, Víctor A. Lórenz-Fonfría

Research output: Contribution to journalArticleResearchpeer-review

28 Citations (Scopus)


The melibiose carrier from Escherichia coli (MelB) couples the accumulation of the disaccharide melibiose to the downhill entry of H , Na+, orLi+. In this work, substrate-induced FTIR difference spectroscopy was used in combination with fluorescence spectroscopy to quantitatively compare the conformational properties of MelB mutants, implicated previously in sodium binding, with those of a fully functional Cys-less MelB permease. The results first suggest that Asp55 and Asp59 are essential ligands for Na binding. Secondly, though Asp124 is not essential for Na+ binding, this acidic residue may play a critical role, possibly by its interaction with the bound cation, in the full Na+ -induced conformational changes required for efficient coupling between the ion- and sugar-binding sites; this residue may also be a sugar ligand. Thirdly, Asp19 does not participate in Na+ binding but it is a melibiose ligand. The location of these residues in two independent threading models of MelB is consistent with their proposed role.
Original languageEnglish
Pages (from-to)22078-22083
JournalProceedings of the National Academy of Sciences of the United States of America
Publication statusPublished - 21 Dec 2010


  • Infrared spectroscopy
  • Ligand binding
  • Membrane proteins
  • Sugar/cation symporter


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