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Proc Natl Acad Sci U S A. 2011 Apr 12;108(15):6115-20. doi: 10.1073/pnas.1103027108. Epub 2011 Mar 28.

Tidal surge in the M2 proton channel, sensed by 2D IR spectroscopy.

Author information

1
Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104-6323, USA.

Abstract

The M2 proton channel from influenza A virus transmits protons across membranes via a narrow aqueous pore lined by water and a proton sensor, His37. Near the center of the membrane, a water cluster is stabilized by the carbonyl of Gly34 and His37, the properties of which are modulated by protonation of His37. At low pH (5-6), where M2 conducts protons, this region undergoes exchange processes on the microsecond to second timescale. Here, we use 2D IR to examine the instantaneous conformational distribution and hydration of G34, and the evolution of the ensemble on the femtosecond to picosecond timescale. The channel water is strongly pH dependent as gauged by 2D IR which allows recording of the vibrational frequency autocorrelation function of a (13)C = (18)O Gly34 probe. At pH 8, where entry and exit of protons within the channel are very slow, the carbonyl groups appear to adopt a single conformation/environment. The high-pH conformer does not exhibit spectral dynamics near the Gly34, and water in the channel must form a relatively rigid ice-like structure. By contrast, two vibrational forms of G34 are seen at pH 6.2, neither of which is identical to the high-pH form. In at least one of these low-pH forms, the probe is immersed in a very mobile, bulk-like aqueous environment having a correlation time ca. 1.3 ps at pH 6.2. Thus, protonation of His37 at low pH causes liquid-like water molecules to flow into the neighborhood of the Gly34.

PMID:
21444789
PMCID:
PMC3076828
DOI:
10.1073/pnas.1103027108
[Indexed for MEDLINE]
Free PMC Article

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