Chromoprotein


A chromoprotein is a conjugated protein that contains a pigmented prosthetic group. A common example is haemoglobin, which contains a heme cofactor, which is the iron-containing molecule that makes oxygenated blood appear red. Other examples of chromoproteins include other hemochromes, cytochromes, phytochromes and flavoproteins.
In hemoglobin there exists a chromoprotein, namely heme, consisting of Fe++ four pyrrol rings.
Sea anemones contain purple chromoproteins shCP which are in its trans-conformation. The purple chromoprotein is derived from Glu-63, Tyr-64 and Gly-65 and the phenolic group of Tyr-64 plays a vital role in the formation of a conjugated system with the imidazolidone moiety resulting a high absorbance in the absorption spectrum of chromoprotein in the excited state and the replacement of Tyrosine with other amino acid leads to the alteration of optical property and non-planer properties of chromoprotein. Fluorescent proteins such as anthrozoa chromoproteins emits long wavelengths
A single chromoprotein can act as both a phytochrome and a phototropin due to the presence and processing of multiple chromophores. Phytochrome in ferns contains PHY3 which contains an unusual photoreceptor with a dual-channel possessing both phytochrome and phototropin and this helps the growth of fern plants at low sunlight. The GFP protein family includes both fluorescent proteins and non-fluorescent chromoproteins. Through mutagenesis or irradiation, the non-fluorescent chromoproteins can be converted to fluorescent chromoproteins. An example of such converted chromoprotein is "kindling fluorescent proteins" or KFP1 which was converted from a mutated non-fluorescent Anemonia sulcata chromoprotein to a fluorescent chromoprotein.