Insight into the Mechanism of the Influenza A Proton Channel from a Structure in a Lipid Bilayer

Abstract

The M2 protein from the influenza A virus, an acid-activated proton-selective channel, has been the subject of numerous conductance, structural, and computational studies. However, little is known at the atomic level about the heart of the functional mechanism for this tetrameric protein, a His37-Trp41 cluster. We report the structure of the M2 conductance domain (residues 22 to 62) in a lipid bilayer, which displays the defining features of the native protein that have not been attainable from structures solubilized by detergents. We propose that the tetrameric His37-Trp41 cluster guides protons through the channel by forming and breaking hydrogen bonds between adjacent pairs of histidines and through specific interactions of the histidines with the tryptophan gate. This mechanism explains the main observations on M2 proton conductance.

Viroporins: structure, function and potential as antiviral targets

“…However, the precise mechanism by which protonation induces channel opening remains a matter of debate. His37 protonation stabilizes M2 tetramers and also occurs at much higher pH compared with His in free solution (Hu et al, 2006), supporting a 'dimer of dimers' model for the His37 tetrad where each pair shares a single proton (Sharma et al, 2010). This allows one His of each pair to interact with adjacent Trp41, whereupon a third protonation event induces channel opening via alteration of the helical bundle and opening the Trp41 gate (Chizhmakov et al, 1996;Pielak & Chou, 2010).…”

“…Indeed, conflicting structures of drug-bound M2 have generated considerable controversy over the nature of M2 drug inhibition over recent years (see below). Perhaps the most biologically relevant M2 structure comprises CD peptides in a DOPC/DOPE (dioleoylphosphatidylcholine/dioleoylphosphatidylethanolamine) bilayer at pH 7.5 [Protein Data Bank (PDB) ID: 2LOJ] (Sharma et al, 2010), although no drug molecule was bound. Recent drug-bound studies include a solid-state NMR structure in DMPC (dimyristoylphosphatidylcholine) bilayers with amantadine bound to the channel lumen (PDB ID: 2KQT) (Cady et al, 2009(Cady et al, , 2010, as well as solution structures of CD peptides in detergent micelles with four rimantadine molecules bound to a peripheral, membraneexposed binding site (PDB ID: 2RLF) (Schnell & Chou, 2008).…”

Proton evolved local field solid-state nuclear magnetic resonance using Hadamard encoding: Theory and application to membrane proteins

“…Therefore, the HE-PELF experiment avoids repeating the PELF experiment at several mixing times for the optimal detection of dynamically averaged dipolar couplings, an important detail for flexible or weakly aligned molecular systems. We demonstrated the performance of the PELF for a uniformly 15 N labeled membrane protein.…”

“…10 SLF experiments have been widely used by chemists and biophysicists to characterize the structures of liquid crystals as well as membrane proteins in mechanically or magnetically aligned lipid bilayers. [11][12][13][14][15][16][17][18] Since the introduction of the SLF experiment, several variants have emerged, such as PISEMA, [19][20][21] SAMPI4, 22 HIMSELF, 23 and more recently the sensitivity-enhanced and constant time versions. [24][25][26][27] These experiments are also known as rotating frame SLF (R-SLF) experiments and take advantage of the heteronuclear DC evolution under Hartmann-Hahn matching of RF fields for I and S spins and homonuclear decoupling for the abundant I spins.…”

“…33 In this paper, we present a Hadamard-encoded PELF experiment (or HE-PELF), which can achieve the optimum sensitivity for a wide range of DC values using a single 2D experiment. The advantages of the HE-PELF over the original PELF pulse sequence are demonstrated for a 15 N labeled NAL single crystal and uniformly 15 N labeled sarcolipin oriented in lipid bicelles.…”