Sensory Rhodopsins
The proteins: sensory rhodopins are seven-helical transmembrane
proteins related to the light-driven ion pump bacteriorhodospin
(BR) which contain a retinal
co-factor. They are found in the archaea H. salinarum and
N. pharaonis where they act as phototaxis receptors. Sensory
rhodopsin II (NpSRII) that mediates blue-light avoidance by the haloarchaeon
Natronobacterium pharaonis. The maximum absorption of the
NpSRII all-trans chromophore is significantly blue-shifted with
respect to BR (from 568 nm for BR to 497 nm for NpSRII).
This shift gives rise to the orange color (blue-light absorption) of the
protein. When a blue photon is absorbed by the NpSRII chromphore,
rapid (pico second time scale) isomerization from all-trans to 13-cis,15-anti
takes place. This light-induced shape change of the chromophore in
turn causes the surrounding protein to also change shape. This change
in chape is ultimately sensed by the specific transducer protein called
HtrII, which binds tightly to NpSRII. HtrII then signals to
the ???? [under construction]
The crystals: the crystals are grown from cubic lipid phase
(Landau & Rosenbusch, PNAS, 1996) and form long orange needles:
Fig. 1: NpSRII crystal in cryo loop at ESRF microfocus
beamline ID13
The paper:
Crystal Structure of Sensory Rhodopsin II at 2.4 Å: Insights
into Color Tuning and Transducer Interaction.
H Luecke, B Schobert, JK Lanyi, EN Spudich, JL Spudich (2001) Science
July 12, 2001.
The atomic model:
1jgj.pdb (released
July 12, 2001): 2.4 Å wild-type structure described in the
2001
Science paper.