Chlamyrhodopsin represents a new type of sensory photoreceptor.

Abstract

In order to find optimal light conditions for photosynthetic growth, the green alga Chlamydomonas uses a visual system. An optical device, a rhodopsin photoreceptor and an electrical signal transduction chain that mediates between photoreceptor and flagella comprise this system. Here we present an improved strategy for the preparation of eyespot membranes. These membranes contain a retinal binding protein, which has been proposed to be the apoprotein of the phototaxis receptor. The retinal binding protein, which we named chlamyopsin, was purified and opsin‐specific antibodies were raised. Using these antibodies, the opsin was localized in the eyespot region of whole cells during growth and cell division. The opsin cDNA was purified and sequenced. The sequence reveals that chlamyopsin is not a typical seven helix receptor. It shows some homology to invertebrate opsins but not to opsins from halobacteria. It contains many polar and charged residues and might function as a light‐gated ion channel complex. It is likely that this lower plant rhodopsin diverged from animal opsins early in opsin evolution.

Light-Intensity-Dependent Expression of Lhc Gene Family Encoding Light-Harvesting Chlorophyll-a/b Proteins of Photosystem II in Chlamydomonas reinhardtii

“…This view is consistent with the results that the addition of DCMU and the deletion of the PS little affected the low-light accumulation. Although phytochrome has not been reported in C. reinhardtii, a protein with retinal as chromophore (chlamyopsin; Deininger et al, 1995) and a homolog of cryptochrome (CPH1; Small et al, 1995) have been identified. Kindle (1987) proposed that the light-induced expression of a Lhc gene is controlled by a system with a blue-light receptor rather than by a phytochrome in C. reinhardtii, although the photoreceptor has not yet been identified.…”

Algal photoreceptors: in vivo functions and potential applications

“…Further experiments in Peter Hegemann's group led to the identification of the first rhodopsin gene (Cop); alternative splicing of the Cop premRNA leads to two protein variants, CR1 (235 amino acid residues) and CR2 (243 amino acid residues). Although the amino acid sequences of CR1 and CR2 show a high degree of sequence identity (~91 %), both proteins have different hypothetical retinal-binding sites (Deininger et al 1995;Fuhrmann et al 2003). Both proteins are strongly enriched in the eyespot of Chlamydomonas; however, the concentration of CR2 is about 50-fold higher than the concentration of CR1 (Deininger et al 1995;Fuhrmann et al 2003).…”

“…Although the amino acid sequences of CR1 and CR2 show a high degree of sequence identity (~91 %), both proteins have different hypothetical retinal-binding sites (Deininger et al 1995;Fuhrmann et al 2003). Both proteins are strongly enriched in the eyespot of Chlamydomonas; however, the concentration of CR2 is about 50-fold higher than the concentration of CR1 (Deininger et al 1995;Fuhrmann et al 2003). Although the abundant variant, CR2, was expected to be the responsible photoreceptor for light-induced movements in Chlamydomonas, no changes in phototaxis and photophobic responses were observed in transgenic strains with a reduced concentration of this protein ( Fuhrmann Fig.…”

Two rhodopsins mediate phototaxis to low- and high-intensity light in Chlamydomonas reinhardtii

“…Fitting with a sum of two saturating functions reveals a slower low-light-saturating current and faster high-light-saturating current (9-11, 16, 17), which were interpreted as being driven by either a single, or two different, photoreceptor proteins (18). Multiple photoreceptors have been considered, based on the complex shape of the photoreceptorcurrent action spectrum (8,11,14), and results from retinalreconstitution studies (19).For several years the most abundant protein in the eyespot membranes of Chlamydomonas and Volvox has been considered as the photoreceptor for photomotile responses in these algae (20,21). However, recently the so-called ''chlamyrhodopsin'' (21) has been ruled out as the photoreceptor pigment for either phototaxis or the photophobic response in Chlamydomonas (22).…”