Why not a new post about the fluorescent proteins? An interesting topic after the discovery of the Super Coral, a green fluorescent hybrid belonging to Acropora which is a rare feature for species belonging to this genus in Caribbean Sea.
Corals are highly appreciated from hobbyist for their vivid coloration, for which fluorescent proteins are largely responsible. A wide array of fluorescent proteins has been described within anthozoans, ranging across three basic color types : cyan, green and red. Because of their ability to convert wavelengths of day light, the most prominent hypothesis about the function of fluorescent proteins within corals is related to the maintenance of the symbiosis with dinoflagellates, commonly known as zooxanthellae, and it has been proposed photoprotective and/or light enhancing roles.
Another fluorescent protein function includes cell protection against oxygen free radicals. Free radicals are reactive oxygen molecules such as hydrogen peroxide (H2O2) that result from the regulation of cellular redox process. Free radicals are produced by a number of cellular pathways including by photosynthesis of dinoflagellate symbionts. At low concentrations, free radicals might exert positive effects on the coral cells, for instance in immune function, but high levels of free radicals and oxidants generate oxidative stress that can damage cell structures, including interactions with lipids, proteins, and DNA. H2O2 is particularly attributed to the induction of oxidative stress , as it is the most stable of the oxygen species and easily diffuses across biological membranes. The photosynthetic zooxanthellae generate high quantities of dissolved oxygen under normal conditions, but coral is protected by antioxydant effect of fluorescent proteins. However, during thermal or light stress events, the hydrogen peroxide level increases, inducing oxidative stress in both the symbiont and the coral host, the so-called ‘bleaching’. Injury or protozoan infection also contributes to elevated H2O2 level in coral tissues, thus increasing the risk of bleaching. Interestingly, up regulation of fluorescent proteins occurs in injured coral tissue, illustrating the role of these proteins in coral stress responses.
Pigmentation responses of a) A. millepora with blue pigmentation in response to breakage and b) Porites massive sp. with pink pigmentation in response to fish bites. After Palmer, Modi & Mydlarz. Coral fluorescent proteins as antioxidants. PLoS One 2009 Oct 6;4(10).
Oxidative stress plays a major role in the development of cancer, autoimmune disorders and neurodegenerative diseases in human and there is an increasing interest in finding new antioxidant molecules, because they can inhibit the propagation of free radical reactions, responsible for these diseases. As it is well known now, the coral reefs are natural pharmacy. Animals developed a lot of active substances during their evolution in the coral reefs. Our favorite animals are then very good candidates for studying oxidative stress in the cell and might open new research fields for human well being.