title: FTIR spectroscopy of secondary-structure reorientation of melibiose permease modulated by substrate binding.
abstract: Analysis of infrared polarized absorbance spectra and linear dichroism spectra of reconstituted melibiose permease from Escherichia coli shows that the oriented structures correspond mainly to tilted transmembrane alpha-helices, forming an average angle of approximately 26 degrees with the membrane normal in substrate-free medium. Examination of the deconvoluted linear dichroism spectra in H(2)O and D(2)O makes apparent two populations of alpha-helices differing by their tilt angle (helix types I and II). Moreover, the average helical tilt angle significantly varies upon substrate binding: it is increased upon Na(+) binding, whereas it decreases upon subsequent melibiose binding in the presence of Na(+). In contrast, melibiose binding in the presence of H(+) causes virtually no change in the average tilt angle. The data also suggest that the two helix populations change their tilting and H/D exchange level in different ways depending on the bound substrate(s). Notably, cation binding essentially influences type I helices, whereas melibiose binding modifies the tilting of both helix populations.
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. ndave@imim.es
authors.forename: Natàlia
authors.initials: N
authors.lastname: Dave
authors.forename: Víctor A
authors.initials: VA
authors.lastname: Lórenz-Fonfría
authors.forename: Gérard
authors.initials: G
authors.lastname: Leblanc
authors.forename: Esteve
authors.initials: E
authors.lastname: Padrós
mesh_terms: D002942:Circular Dichroism; D041961:Deuterium Exchange Measurement; D004926:Escherichia coli / Q000201:enzymology*; D008553:Melibiose / Q000378:metabolism*; D011485:Protein Binding; D017433:Protein Structure, Secondary; D012964:Sodium / Q000737:chemistry / Q000494:pharmacology; D017550:Spectroscopy, Fourier Transform Infrared; D027981:Symporters / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D027981:Symporters; C021548:melibiose permease; D008553:Melibiose; D012964:Sodium