Review
doi: 10.1002/pro.2158. Epub 2012 Oct 9.Structural basis for proton conduction and inhibition by the influenza M2 protein
Affiliations
- PMID:23001990
- PMCID: PMC3527700
- DOI: 10.1002/pro.2158
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Review
Structural basis for proton conduction and inhibition by the influenza M2 protein
Mei Hong et al. Protein Sci.2012 Nov.
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Abstract
The influenza M2 protein forms an acid-activated and drug-sensitive proton channel in the virus envelope that is important for the virus lifecycle. The functional properties and high-resolution structures of this proton channel have been extensively studied to understand the mechanisms of proton conduction and drug inhibition. We review biochemical and electrophysiological studies of M2 and discuss how high-resolution structures have transformed our understanding of this proton channel. Comparison of structures obtained in different membrane-mimetic solvents and under different pH using X-ray crystallography, solution NMR, and solid-state NMR spectroscopy revealed how the M2 structure depends on the environment and showed that the pharmacologically relevant drug-binding site lies in the transmembrane (TM) pore. Competing models of proton conduction have been evaluated using biochemical experiments, high-resolution structural methods, and computational modeling. These results are converging to a model in which a histidine residue in the TM domain mediates proton relay with water, aided by microsecond conformational dynamics of the imidazole ring. These mechanistic insights are guiding the design of new inhibitors that target drug-resistant M2 variants and may be relevant for other proton channels.
Copyright © 2012 The Protein Society.
Figures
(A) Functional model of the TM domain of the M2 tetramer, showing the positions of crucial side chains and the drug amantadine. The model was obtained from cysteine scanning mutagenesis., (B) High-resolution structure of the amantadine-bound M2TM in DMPC bilayers obtained from SSNMR (PDB: 2KQT). The overall shape of the tetrameric bundle from the functional model is in excellent agreement with the high-resolution structure; however, specific differences exist such as the helix tilt angle and the conformations of several side chains (e.g., Ser31 and Trp41). In both images, the “front” helix has been removed for clarity.
Structures of the TM domain of M2. (A) The N-terminal pore is lined by the hydroxyl of Ser31 and backbone carbonyl groups (pictured structure is the 1.65 Å crystal structure at pH 6.5, PDB: 3LBW). The molecular surface of the channel is color-coded with the oxygen atoms in red, carbon in gray, and nitrogen in blue. The “front” helix has been removed for clarity. (B) Superimposed solid-state NMR structure at pH 7.5 (2L0J, yellow), the 1.65-Å crystal structure at pH 6.5 (3LBW, blue), and the 3.5-Å crystal structure at pH 5.3 (3C9J, red). His37 and Trp41 side chains (sticks) and Gly34 Cα (ball) are shown.
(A) The proton conduction pathway seen in a 1.65-Å resolution crystal structure including three clusters of crystallographic waters. (B–D) A second perspective of the outer (B), bridging (C), and exit (D) clusters viewed normal to the membrane plane. (E) The surface of the pore (light blue shading) is shown along with the crystallographic waters (red spheres). Val27, His37, and Trp41 residues are rendered in blue, orange, and magenta, respectively. Pore radius profiles are plotted for the high-resolution crystal structure (3LBW, blue solid line), low-pH (3C9J, blue dash-dotted line), and amantadine-inhibited (red dashed line) structures.
The Trp41 rotamer and Trp41-Asp44 contact in the (A) high pH, drug-bound solution NMR structure (2RLF), and (B) the pH 6.5 X-ray crystal structure (3LBW). A larger pore radius at Trp41 is found in B due to the 180° χ2 angle change. The Trp41 side chains are shown in spheres for Trp41 (green for C, blue for N), and in ball-and-stick for Asp44 (pink C, blue O). His37 is shown as spheres with orange for C, blue for N. His37′s side chain is almost fully occluded by Trp41 in (A); in (B), it has slightly more accessibility. Crystallographically defined water molecules are shown in small red spheres in B, with hydrogen bonds shown in dashed lines.
Snapshot from a simulation of amantadine with WT (far left). Water molecules (red) associate with carbonyl groups (green/red sticks) in a square planar array. This array of water molecules can stabilize the bound ammonium group of amantadine (green and blue bound drug) or a centrally located water molecule (magenta). The remaining panels show vertical slices of the channel in schematic form, showing how a longer inhibitor than amantadine places its ammonium group deeper in the channel and displaces more water molecules.
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References
- Gandhi CS, Shuck K, Lear JD, Dieckmann GR, DeGrado WF, Lamb RA, Pinto LH. Cu(II) inhibition of the proton translocation machinery of the influenza A virus M2 protein. J Biol Chem. 1999;274:5474–5482. - PubMed