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Emerging Concepts in Ion Channel Biophysics
Poster Abstracts
49
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.