Campus Units

Chemistry

Document Type

Article

Publication Version

Accepted Manuscript

Publication Date

9-2009

Journal or Book Title

Journal of Biomolecular NMR

Volume

45

Issue

1-2

First Page

185

Last Page

196

DOI

10.1007/s10858-009-9352-9

Abstract

The molecular motions of membrane proteins in liquid-crystalline lipid bilayers lie at the interface between motions in isotropic liquids and in solids. Specifically, membrane proteins can undergo whole-body uniaxial diffusion on the microsecond time scale. In this work, we investigate the H-1 rotating-frame spin-lattice relaxation (T-1 rho) caused by the uniaxial diffusion of the influenza AM2 transmembrane peptide (M2TMP), which forms a tetrameric proton channel in lipid bilayers. This uniaxial diffusion was proved before by H-2, N-15 and C-13 NMR lineshapes of M2TMP in DLPC bilayers. When bound to an inhibitor, amantadine, the protein exhibits significantly narrower linewidths at physiological temperature. We now investigate the origin of this line narrowing through temperature-dependent H-1 T-1 rho relaxation times in the absence and presence of amantadine. Analysis of the temperature dependence indicates that amantadine decreases the correlation time of motion from 2.8 +/- 0.9 mu s for the apo peptide to 0.89 +/- 0.41 ls for the bound peptide at 313 K. Thus the line narrowing of the bound peptide is due to better avoidance of the NMR time scale and suppression of intermediate time scale broadening. The faster diffusion of the bound peptide is due to the higher attempt rate of motion, suggesting that amantadine creates better-packed and more cohesive helical bundles. Analysis of the temperature dependence of ln(T-1 rho(-1)) indicates that the activation energy of motion increased from 14.0 +/- 4.0 kJ/mol for the apo peptide to 23.3 +/- 6.2 kJ/mol for the bound peptide. This higher activation energy indicates that excess amantadine outside the protein channel in the lipid bilayer increases the membrane viscosity. Thus, the protein-bound amantadine speeds up the diffusion of the helical bundles while the excess amantadine in the bilayer increases the membrane viscosity.

Comments

This is a post-peer-review, pre-copyedit version of an article published in Journal of Biomolecular NMR. The final authenticated version is available online at: http://dx.doi.org/10.1007/s10858-009-9352-9. Posted with permission.

Copyright Owner

Springer Science+Business Media B.V.

Language

en

File Format

application/pdf

Published Version

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