FIAS Scientific Report 2011 - Frankfurt Institute for Advanced Studies ...

Solution NMR structure of proteorhodopsin
Collaborators: Sina Reckel 1 , Daniel Gottstein 1,2 , Jochen Stehle 3 , Frank Löhr 1 , Mirka-Kristin Verhoefen 4 ,
Mitsuhiro Takeda 5 , Robert Silvers 4 , Masatsune Kainosho 5 , Clemens Glaubitz 1 , Josef Wachtveitl 4 , Frank
Bernhard 1 , Harald Schwalbe 3 , Peter Güntert 1,2 , Volker Dötsch 1
1 Institute of Biophysical Chemistry and Center for Biomolecular Magnetic Resonance, Goethe University Frankfurt am
Main, 2 Frankfurt Institute for Advanced Studies, 3 Institute for Organic Chemistry and Chemical Biology and Center
for Biomolecular Magnetic Resonance, Goethe University Frankfurt am Main, 4 Institute of Physical and Theoretical
Chemistry, Goethe University Frankfurt am Main, 5 Structural Biology Research Center, Nagoya University, Japan
Green-absorbing proteorhodopsin (PR), a light-driven proton pump, shows a strong dependence of its function
on the pH. The primary proton acceptor D97 has an unusually high pKa value around 7.5 and its protonation
state affects the absorption characteristics of the retinal cofactor. Furthermore, the direction of proton
pumping switches in response to pH between an outward directed transport at alkaline pH and an inward directed
transport at acidic pH. The potential function of this pH-dependency including the changing vectoriality
is, however, still debated and a possible regulatory activity cannot be excluded. For a further insight into the
structure-function relationship, we have solved the solution NMR structure of detergent-solubilized PR at acidic
pH. NOE data was obtained with the help of stereo-array isotope labeling (SAIL) as well as selective labeling
and complemented with a large number of distance restraints derived from paramagnetic relaxation enhancement
(PRE). Additionally, restraints from residual dipolar couplings served to improve the structural accuracy
of this seven-helix-bundle. The three-dimensional structure of PR reveals differences from its homologues such
as the absence of the extended β-sheet in the B-C loop and enables insight into the mechanisms of color-tuning
and proton transport.
Figure: Structure of Proteorhodopsin. a) Bundle of the 20 conformers with lowest CYANA target function obtained from
structure calculation. Helices are color-coded from helix A in dark blue to helix G in red. b) Cartoon representation of
the conformer with the lowest CYANA target function seen from the side and from the top. In the lower panel helices are
additionally labeled A-G.
Related publications in 2011:
1) Reckel, S., Gottstein, D., Stehle, J., Löhr, F., Verhoefen, M. K., Takeda, M., Silvers, R., Kainosho, M.,
Glaubitz, C., Wachtveitl, J., Bernhard, F., Schwalbe, H., Güntert, P., Dötsch, V. Solution NMR structure of
proteorhodopsin. Angew. Chem. Int. Ed. 50, 11942–11946 (2011)
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