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Rhodopsin-mediated photoreception in cryptophyte flagellates.
Oleg A Sineshchekov1, Elena G Govorunova, Kwang-Hwan Jung
1Center for Membrane Biology, Department of Biochemistry and Molecular Biology, University of Texas Medical School, Houston, Texas 77030, USA. oleg_sinesh@yahoo.com
Biophysical Journal
|September 10, 2005
Summary
Cryptophyte algae likely use a two-rhodopsin system for phototaxis, similar to green algae. Researchers identified and characterized these algal rhodopsins, revealing their unique properties and potential roles in light sensing.
Area of Science:
- Photobiology
- Algal Physiology
- Molecular Biology
Background:
- Phototaxis, the light-directed movement, is crucial for algal survival and distribution.
- Rhodopsins are light-sensitive proteins involved in various sensory processes.
- Previous studies suggested rhodopsins mediate phototaxis in some algae, but the exact mechanisms in cryptophytes remained unclear.
Purpose of the Study:
- To investigate the molecular mechanisms underlying phototaxis in marine and freshwater cryptophytes.
- To characterize the spectroscopic and functional properties of cryptophyte algal rhodopsins.
- To identify and compare rhodopsin genes in cryptophyte species.
Main Methods:
- Spectroscopic analysis of isolated rhodopsins.
- Electrophysiological recordings of photoreceptor currents.
- Gene sequencing and expression analysis of opsin proteins.
- Phototaxis assays with varying light conditions and inhibitors.
Main Results:
- Cryptophytes exhibit phototaxis with peak sensitivities around 450 nm and above 500 nm, suggesting two photoreceptor systems.
- Two novel type 1 opsin genes were identified in Guillardia theta, and one in Cryptomonas sp.
- Characterization of a G. theta rhodopsin (GtR1) revealed slow turnover kinetics and no proton pumping activity in E. coli, but its absorption spectrum aligns with phototaxis sensitivity.
- A second G. theta rhodopsin (GtR2) and the Cryptomonas rhodopsin possess structural features consistent with known sensory rhodopsins.
Conclusions:
- Cryptophyte phototaxis is likely mediated by a two-rhodopsin photosensory mechanism, analogous to that in Chlamydomonas reinhardtii.
- The identified rhodopsins are potential candidates for mediating the observed phototactic responses in cryptophytes.
- This study provides the first detailed biophysical characterization of cryptophyte algal rhodopsins.