Structural insights into the early steps of receptor-transducer signal
transfer in archaeal phototaxis.

 Wegener AA, Klare JP, Engelhard M, Steinhoff HJ.

Max-Planck-Institut fur Molekulare Physiologie, Otto Hahn-Strasse 11, D-44227 Dortmund,
Germany Present address: Preclinical R&D, Merck KGaA, D-64271 Darmstadt, Germany
Corresponding author e-mail: martin.engelhard@mpi-dortmund.mpg.de

Electron paramagnetic resonance-based inter-residue distance measurements between
site-directed spin-labelled sites of sensory rhodopsin II (NpSRII) and its transducer NpHtrII
from Natronobacterium pharaonis revealed a 2:2 complex with 2-fold symmetry. The core of
the complex is formed by the four transmembrane helices of a transducer dimer. Upon light
excitation, the previously reported flap-like movement of helix F of NpSRII induces a
conformational change in the transmembrane domain of the transducer. The inter-residue
distance changes determined provide strong evidence for a rotary motion of the second
transmembrane helix of the transducer. This helix rotation becomes uncoupled from changes
in the receptor during the last step of the photocycle.
EMBO J 2001 Oct 1;20(19):5312-9