title: Changes in secondary structures and acidic side chains of melibiose permease upon cosubstrates binding.
abstract: Infrared difference spectroscopy analysis of the purified melibiose permease of Escherichia coli reconstituted into liposomes was carried out as a function of the presence of the two symporter substrates (Na(+), melibiose) in either H(2)O or in D(2)O media. Essentially, the data first show that addition of Na(+) induces appearance of peaks assigned to changes in the environment and/or orientation of alpha-helical domains of purified melibiose permease. Likewise, melibiose addition in the presence of Na(+) produces peaks corresponding to additional changes of alpha-helix environment or tilt. In addition to these changes, a pair of peaks (1599 (+) cm(-1)/1576 (-) cm(-1)) appearing in the Na(+)-induced difference spectrum is assigned to the antisymmetric stretching of COO(-) groups, since they show practically no shift upon H/D exchange. It is proposed that these acidic groups participate in Na(+) co-ordination. A corresponding pair of peaks, again fairly insensitive to H/D substitution (1591 (-) cm(-1)/1567 (+) cm(-1)), appear in the melibiose-induced difference spectra, and may again be assigned to COO(-) groups. The latter carboxyl groups may correspond to part or all of the acidic residues interacting with Lys or Arg in the resting state that become free upon melibiose binding.
authors.affiliation: Unitat de Biofísica, Departament de Bioquímica i de Biologia Molecular, Facultat de Medicina, and Centre d'Estudis en Biofísica, Universitat Autònoma de Barcelona, Barcelona, Spain.
authors.forename: Xavier
authors.initials: X
authors.lastname: León
authors.forename: Raymonde
authors.initials: R
authors.lastname: Lemonnier
authors.forename: Gérard
authors.initials: G
authors.lastname: Leblanc
authors.forename: Esteve
authors.initials: E
authors.lastname: Padrós
mesh_terms: D020816:Amino Acid Motifs; D003903:Deuterium; D029968:Escherichia coli Proteins / Q000737:chemistry*; D008081:Liposomes / Q000737:chemistry*; D008239:Lysine / Q000737:chemistry; D008553:Melibiose / Q000737:chemistry; D011485:Protein Binding; D017433:Protein Structure, Secondary; D012964:Sodium / Q000737:chemistry; D017550:Spectroscopy, Fourier Transform Infrared; D013379:Substrate Specificity; D027981:Symporters / Q000737:chemistry*; D014867:Water / Q000737:chemistry
chemical_list: D029968:Escherichia coli Proteins; D008081:Liposomes; D027981:Symporters; D014867:Water; C021548:melibiose permease; D008553:Melibiose; D012964:Sodium; D003903:Deuterium; D008239:Lysine