Photoreceptor proteins are light-sensitive proteins involved in the sensing and response to light in a variety of organisms.[1] Photoreceptor proteins can be find in both animals and plants. Human eye retina is a good example of photoreceptor protein. Many bacteria, such as halohodospira halophila, an extremophile bacterium contain Photoactive Yellow Protein. Photoreceptor proteins are optimally suited to study the role of dynamical alterations in protein structure in relation to their function. First, such proteins can be triggered with (laser) flash illumination, and therefore excellent time-resolution is achievable in studies of the dynamical alterations in their structure. Second, because they are signal-transduction proteins, one may anticipate large conformational transitions to be involved in their signaling state formation (and its subsequent decay), which is indeed borne out by the experiments. Third, the (changing) color of these proteins often is an excellent indicator as to which time scale is relevant to resolve structural transitions. Significant and unsurpassed insight along these lines has been obtained for a number of different photoreceptor proteins. Hence, they can, indeed, be considered as “star actors” in the pursuit to understand, in general terms, the atomic details of the dynamics of functional conformational transitions [i.e., (partial) un/folding] in these proteins required for their functioning.[4] Structure Photoreceptor protein contains two parts, the protein part, and non-protein, chromophore part. The non-protein part can response to light throught photoisomerization, or photoexcitation. [2] The figure above show protein part in secondary structure, and chromophorepart in line structure. Photoreceptor in Plants Plants are important living organisms on earth. As autotrophs, part of plants absorb sunlight through photosynthesis to convert water and Carbon dioxide to oxygen and other chemicals. The part of plants that responsible for absorb and use sunlight is photoreceptor. There are many types of photoreceptors in plants, such as Chlorophyll. PHYTOCHROMES BLUE-LIGHT RECEPTORS In plant seeds, the photoreceptor phytochrome is responsible for the process termed photomorphogenesis. This occurs when a seed initially situated in an environment of complete darkness is exposed to light. A brief exposure to electromagnetic radiation, particularly that whose wavelength is within the red and far-red lights, results in the activation of the photorecepter phytochrome within the seed. This in turn sends a signal through the signal transduction pathway into the nucleus, and triggers hundreds of genes responsible for growth and development.[3] References "Photoreceptor Protein." Wikipedia . Wikimedia Foundation, 21 Jan. 2013. Web. 04 Mar. 2013. "Biological Photoreceptors." Biological Photoreceptors . N.p., n.d. Web. 04 Mar. 2013. Photoreceptors in Plant Photomorphogenesis to Date. Five Phytochromes, Two Cryptochromes, One Phototropin, and One Superchrome, Winslow R. Briggs and Margaret A. Olney, Plant Physiology, January 2001, Vol. 125, pp. 85–88, www.plantphysiol.org © 2001 American Society of Plant Physiologists. Van Der Horst, Michael A., and Klaas J. Hellingwerf. "Photoreceptor Proteins, “Star Actors of Modern Times”: A Review of the Functional Dynamics in the Structure of Representative Members of Six Different Photoreceptor Families." Accounts of Chemical Research 37.1 (2004): 1 Made by S. Jähnichen the Wikipediaproject. Jmol Development Team, Phytochrome, 4/12/2011, Wikipedia. BrautigamCA, Smith BS, Ma Z, PalnitkarM, TomchickDR, MachiusM, Deisenhofer J (August 2004). "Structure of the photolyase-like domain of cryptochrome1 from Arabidopsis thaliana". Proc. Natl. Acad. Sci. U.S.A. 101 (33): 12142–7. doi:10.1073/pnas.0404851101. PMC 514401. PMID 15299148. Hitomi, K.; Okamoto, K.; Daiyasu, H.; Miyashita, H.; Iwai, S.; Toh, H.; Ishiura, M.; Todo, T. Bacterial cryptochrome and photolyase: characterization of two photolyase-like genes of Synechocystis sp. PCC6803. Nucleic Acids Res. 2000, 28, 2353-2362.