Article

FTIR Spectroscopy of Secondary-Structure Reorientation of Melibiose Permease Modulated by Substrate Binding

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.
Biophysical Journal (Impact Factor: 3.97). 06/2008; 94(9):3659-70. DOI: 10.1529/biophysj.107.115550
Source: PubMed

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.

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