Biophysical Society Conference | Tahoe 2023

Proton Reactions: From Basic Science to Biomedical Applications

Monday Speaker Abstracts

PULLING THE STRINGS OF PROTON CONDUCTION: MECHANICAL REGULATION OF VOLTAGE-GATED PROTON CHANNELS Chang Zhao 1 ; Parker D Webster 1 ; Alexis De Angeli 2 ; Francesco Tombola 1 ; 1 University of California, Irvine, Department of Physiology & Biophysics, Irvine, CA, USA 2 University of Montpellier, CNRS, INRAE, 2IPSiM, Institut Agro, Montpellier, France Swelling-induced potentiation of Hv1-mediated proton current was previously proposed to contribute to brain damage after ischemic stroke through excessive activation of the NADPH oxidase in microglial cells. The mechanism underlying Hv1 potentiation is unknown, but it is believed to involve a transition from a state with normal activity to a state with facilitated activation, induced by the mechanical stimulus. Here, we describe an Hv homolog in the angiosperm plant Arabidopsis thaliana that gates with a unique modality as it is activated by an electrical stimulus if it is first exposed to membrane stretch in a process that we call priming. The homolog from another angiosperm, T. cacao, shares the requirement for mechanical priming, whereas homologs from the non-flowering plants P. sitchensis and S. moellendorffii do not, as they can be activated by the electrical stimulus alone. Guided by AI-generated structural models of plant Hv proteins, we swapped protein regions and individual residues between Hvs from A. thaliana and P. sitchensis, and measured the response of the resulting channels to mechanical stimulation. We identified a set of residues that play a crucial role in mechanical priming and propose that Hvs from angiosperm plants require priming because they contain a network of hydrophilic/charged residues that locks the channels in a silent resting state. The mechanical stimulus destabilizes the network allowing the conduction pathway to turn on. Such network appears to be fragmented, and therefore constitutively destabilized, in Hv channels from non flowering plants. Conformations similar to the silent state of Arabidopsis Hv might exist in animal homologs. These states may be sufficiently stable to inhibit channel activation by membrane depolarization but not stable enough to prevent opening altogether. The mechanical stimulus could then destabilize these states, as it is proposed for Arabidopsis Hv, resulting in a facilitated opening.

16