Comparative study of phototactic and photophobic receptor chromophore properties in Chlamydomonas reinhardtii

• Published in: Biophysical journal Vol. 65; no. 1; pp. 508 - 518
• Main Authors: Zacks, D.N., Derguini, F., Nakanishi, K., Spudich, J.L.
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Elsevier Inc 01.07.1993; Biophysical Society
• Subjects: Algorithms; ANALOGS; Analytical, structural and metabolic biochemistry; Animals; Biological and medical sciences; Biophysical Phenomena; Biophysics; Cell Movement - drug effects; Cell Movement - physiology; Cell Movement - radiation effects; Cell physiology; Chlamydomonas reinhardtii; Chlamydomonas reinhardtii - drug effects; Chlamydomonas reinhardtii - physiology; Chlamydomonas reinhardtii - radiation effects; CHLOROPHYCEAE; Freshwater; Fundamental and applied biological sciences. Psychology; ISOMERS; Models, Biological; Molecular and cellular biology; Motility and taxis; MOUVEMENT; MOVEMENT; MOVIMIENTO; ORGANE DES SENS; ORGANOS SENSORIALES; Other biological molecules; Photic Stimulation; PHOTOPHOBOTAXIS; Photoreceptor Cells - drug effects; Photoreceptor Cells - physiology; Photoreceptor Cells - radiation effects; PHOTORECEPTORS; PHOTOTAXIS; RETINAL; Retinaldehyde - analogs & derivatives; Retinaldehyde - chemistry; Retinaldehyde - pharmacology; RETINOL; SENSE ORGANS; Stereoisomerism; TAXIE; TAXIS; Terpenes, steroids. Hormones; Light effect; Photoreception; Algae; Chlorophycophyta; Environmental factor; Structure function relationship; Phototaxis; Chlamydomonas reinhardtii; Photophobia; Taxis; Retinal; Comparative study; Thallophyta; Chromophore
• ISSN: 0006-3495; 1542-0086
• DOI: 10.1016/S0006-3495(93)81067-1

The motile, unicellular, eukaryotic alga Chlamydomonas reinhardtii exhibits two distinct behavioral reactions to light stimuli, phototaxis and the photophobic response. Both are mediated by retinal-containing receptors. This paper focuses on a direct comparison of the two photoresponses and the chromophore requirements for their photoreceptor(s). Using computerized motion analysis assays for phototaxis and photophobic responses by the same populations of cells, we measured the ability of various isomers and analogues of retinal to reconstitute photobehavior in the pigment-deficient mutant FN68. The results indicate that photophobic and phototaxis responses each require chromophores with an all-trans polyene chain configuration, planar ionone ring/polyene chain conformation, and the ability to isomerize around the retinal C13-C14 double bond. One difference between the two behaviors is that the photophobic response becomes highly desensitized after light stimuli to which the phototaxis response does not become desensitized, indicating the existence of at least one distinct step in the photophobic response pathway. A second difference is that the retinal regeneration of the photophobic response but not of phototaxis is inhibited by a 5-membered ring 13-trans-locked analogue. While showing close similarity in the chromophore structural requirements of the two behaviors, the results indicate that differences exist between the two responses at the level of their photoreceptor proteins and/or in their transduction processes.