Emerging Concepts in Ion Channel Biophysics

Emerging Concepts in Ion Channel Biophysics

Poster Abstracts

31-POS Board 31 Structure Guided Transformation of a Light-activated Proton Pump into a Proton Channel Roman Fudim 1 , Michael Szczepek 2 , Arend Vogt 1 , Johannes Vierrock 1 , Scheerer Patrick 2 , Peter Hegemann 1 . 1 Humboldt Universität Berlin, Berlin, Germany, 2 Charité – Universitätsmedizin Berlin, Berlin, Germany. Recently, we introduced the microbial rhodopsin from Coccomyxa subellipsodea (CsR) as a versatile tool to study light-driven proton pumps under electro-chemical load. Here we present the crystal structure of the wildtype rhodopsin in dark state with a resolution of 2.1Å. The structure revealed a unique interaction between the highly conserved Arg83 and the non- conserved Tyr14. This allowed the structure guided design of a passive symmetric proton channel at physiological conditions, by replacement of Tyr14 with a negatively charged Glu, likely causing a transient salt-bridge formation between Arg83 and Glu14 within the photocycle of the rhodopsin.With further electrophysiological and spectroscopic studies we were able to link distinct current components to photocycle intermediates and could show that pump and channel currents occur sequentially in the same molecule emphasizing the role of Arg83 in maintaining unidirectionality. These findings can be valuable for a more generalized understanding of the molecular constraints distinguishing pump from channel currents.

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