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


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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Available from: Víctor A Lórenz-Fonfría, Jan 23, 2015
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    • "Therefore we considered the second derivative profiles of the fit envelope in comparison to the original spectra as well (Fig. 3B and D). The band located at 1655 cm −1 is attributed to the α-helical content [20] [37], while the bands at 1634 and 1639 cm −1 are assigned to unordered structure, and/or loops in hydrophilic regions outside the membrane as well as solvated short helices and/or 3 10 helices [20] [38] [39]. The peak at 1681 and 1674 cm −1 can be attributed to hydrogen bonded turns or closed loops buried in the hydrophobic region, located most likely in the membrane, thus unaffected from 2 H 2 O-buffer. "
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