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Jessica L Thomaston

Jessica L Thomaston

UCSF, USA

Title: XFEL structures of the M2 proton channel of influenza A reveal pH-dependent water networks under room temperature conditions

Biography

Biography: Jessica L Thomaston

Abstract

The M2 proton channel of influenza A is a drug target that is essential for replication of the flu virus. It is also a model system for the study of selective, unidirectional proton transport across a membrane. Ordered water molecules arranged in “wires” inside the channel pore have been proposed to play a role in the conduction of protons to the four gating His37 residues and the stabilization of multiple positive charges within the channel. Previous crystallographic structures determined using a synchrotron radiation source were biased by cryogenic data collection conditions, and room-temperature data collection was limited by radiation damage. These problems have been avoided through room temperature diffraction at an X-ray free electron laser (XFEL).

Data were collected at an XFEL source to a resolution of 1.4 Å at three different pH conditions: pH 5.5, pH 6.5, and pH 8.0. Here, we examine the ordering of water in the M2 pore within crystals containing only the Copen conformation, which is an intermediate that accumulates at high protonation of the His37 tetrad. This allows us to access multiple protonation states of His37 in the Copen conformation and probe changes in solvent ordering prior to and following the release of a proton into the viral interior.

At pH 5.5, a continuous hydrogen bonded network of water molecules spans the vertical length of the channel, consistent with a Grotthuss mechanism model for proton transport to the His37 tetrad. This ordered solvent at pH 5.5 could act to stabilize the positive charges that build up on the gating His37 tetrad during the proton conduction cycle. The number of ordered pore waters decreases at higher pH, where the Copen state is less stable.  These studies provide a graphical view of the response of water to a change in charge within a restricted channel environment.

References:

  1. "XFEL structures of the M2 proton channel of influenza A reveal pH-dependent water networks under room temperature conditions." Thomaston JL, Woldeyes RA, Nakane T, Yamashita A, Tanaka T, Koiwai K, Brewster AS, Barad BA, Chen Y, Lemmin T, Uervirojnangkoorn M, Arima T, Kobayashi J, Masuda T, Suzuki M, Sugahara M, Sauter NK, Tanaka R, Nureki O, Tono K, Joti Y, Nango E, Iwata S, Yumoto F, Fraser JS, DeGrado WF. In press, PNAS July 2017.
  2. "Crystal structure of the drug-resistant S31N influenza M2 proton channel." Thomaston JL, DeGrado WF. Protein Science 25(8):1551-4. August 2016.
  3. "High resolution structures of the M2 proton channel from influenza A virus reveal dynamic          pathways for proton stabilization and transduction." Thomaston JL, Alfonso-Prieto M, Woldeyes R, Fraser JS, Klein ML, Fiorin G, DeGrado WF. PNAS 112(46):14260-5. November 2015.
  4. "Detection of drug-induced conformational change of a transmembrane protein in lipid bilayers using site-directed spin labeling." Thomaston JL, Nguyen P, Brown EC, Upshur MA, Wang J, DeGrado WF, Howard KP. Protein Science 22(1): 65–73. January 2013.