1. Department of Molecular Physiology and Biological Physics, and Center for Structural Biology, University of Virginia, Charlottesville, Virginia 22906, USA
2. Department of Pharmacology, Queen Elizabeth II Medical Center, University of Western Australia, Crawley, Western Australia 6009, Australia
3. Permanent address: Department of Chemistry, Faculty of Science, Chulalongkorn University, Phayathai Rd, Prathumwan, Bangkok 10330, Thailand.

Correspondence to: Eduardo Perozo¹ Correspondence and requests for materials should be addressed to E.P. (e-mail: Email: eperozo@virginia.edu).

Abstract

Mechanosensitive channels act as membrane-embedded mechano-electrical switches, opening a large water-filled pore in response to lipid bilayer deformations. This process is critical to the response of living organisms to direct physical stimulation, such as in touch, hearing and osmoregulation. Here, we have determined the structural rearrangements that underlie these events in the large prokaryotic mechanosensitive channel (MscL) using electron paramagnetic resonance spectroscopy and site-directed spin labelling. MscL was trapped in both the open and in an intermediate closed state by modulating bilayer morphology. Transition to the intermediate state is characterized by small movements in the first transmembrane helix (TM1). Subsequent transitions to the open state are accompanied by massive rearrangements in both TM1 and TM2, as shown by large increases in probe dynamics, solvent accessibility and the elimination of all intersubunit spin–spin interactions. The open state is highly dynamic, supporting a water-filled pore of at least 25 Å, lined mostly by TM1. These structures suggest a plausible molecular mechanism of gating in mechanosensitive channels.