English: The crystal structure of the transmembrane proton channel domain of the influenza A M2 protein, showing tetrameric arrangement of helices with a channel-blocking drug, amantadine, located in the center (red). The amino acid residues involved in proton transduction are shown as sticks. The image is oriented with the N-terminus at the top; the bottom points toward the interior of the virus.

Rendered from PDB ID 3C9J, published in:

Jessica L. Thomaston, Mercedes Alfonso-Prieto, Rahel A. Woldeyes, James S. Fraser, Michael L. Klein, Giacomo Fiorin, and William F. DeGrado. (2015) High-resolution structures of the M2 channel from influenza A virus reveal dynamic pathways for proton stabilization and transduction. Proc Natl Acad Sci 112(46): 14260–14265. DOI: 10.1073/pnas.1518493112. URL: http://www.pnas.org/content/112/46/14260