Time-resolved measurements of an ion channel conformational change driven by a membrane phase transition

Abstract

Using temperature-jump infrared spectroscopy, we are able to trigger a gel-to-fluid phase transition in lipid vesicles and monitor in real time how a membrane protein responds to structural changes in the membrane. The melting of lipid domains in 1,2-dimyristoyl-sn-glycero-3-phosphocholine vesicles is observed to occur in as fast as 50 ns, with a temperature dependence characteristic of critical slowing. Gramicidin D (gD) added to the membrane responds primarily to the change in thickness of the membrane on a timescale coincident with the membrane melting. Using structure-based spectral modeling, we assign the conformational changes to compression and rotation of a partially dissociated gD dimer. Free energy calculations indicate that the high rate is a result of near-barrierless diffusion on a protein energy landscape that is radically reshaped by membrane thinning. The structural changes associated with the phase transition are similar to the fluctuation modes of fluid phase membranes, highlighting the importance of understanding the dynamic nature of the membrane environment around proteins.

Protein induced membrane phase transition facilitates leishmania infection

“…It has been reported earlier that the increase in non-hydrogen bonded carbonyl frequency is responsible for the flexibility as well as mobility and this effect can cause bilayer thinning. 14…”

Ion transport mechanism in gramicidin A channels formed in floating bilayer lipid membranes supported on gold electrodes

“…Kota et al [9] determined the orientation of gA in different lipid vesicles using polarized attenuated total reflection infrared spectroscopy and reported that the orientation of the gA molecules depends on the lipid polar head groups and surface hydration. Time-resolved IR spectroscopy was employed by Stevenson et al to study the effect of the lipid phase transition on the conformation of gramicidin within the lipid bilayer [10]. Naik and Krimm applied the normal mode analysis to calculate IR spectra of different gA conformations and demonstrated that the position of the amide I band can be used to identify different conformations [11].…”

The Effect of Calcium and Halide Ions on the Gramicidin A Molecular State and Antimicrobial Activity

“…Conversion between conformers has been studied in lipid environments [ 21 , 22 , 23 , 24 , 25 ]. In membrane lipid environments, the rate of conversion from the double-stranded helical dimer into the channel dimer is dependent on environmental factors, such as temperature and ionic strength [ 21 , 22 , 23 ].…”