Chromoprotein

A chromoprotein is a conjugated protein that contains a pigmented prosthetic group (or cofactor). 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.[1]

In hemoglobin there exists a chromoprotein (tetramer MW:4 x 16.125 =64.500), namely heme, consisting of Fe++ four pyrrol rings.

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 (red-light sensing) and phototropin (blue-light sensing) and this helps the growth of fern plants at low sunlight.[2]

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.[3] 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.[4]

Sea anemones contain purple chromoprotein shCP with its GFP-like chromophore in the trans-conformation. The chromophore 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. The replacement of Tyrosine with other amino acids leads to the alteration of optical and non-planer properties of the chromoprotein. Fluorescent proteins such as anthrozoa chromoproteins emit long wavelengths [4]

References
  1. Fearon, William Robert (1940). An Introduction to Biochemistry. p. 131. ISBN 9781483225395.
  2. Kanegae, T.; Hayashida, E.; Kuramoto, C.; Wada, M. (2006-11-08). "A single chromoprotein with triple chromophores acts as both a phytochrome and a phototropin". Proceedings of the National Academy of Sciences. 103 (47): 17997–18001. Bibcode:2006PNAS..10317997K. doi:10.1073/pnas.0603569103. ISSN 0027-8424. PMC 1693861. PMID 17093054.
  3. Zagranichny, Vasily E.; Rudenko, Natalia V.; Gorokhovatsky, Andrey Yu.; Zakharov, Mikhail V.; Balashova, Tamara A.; Arseniev, Alexander S. (2004). "Traditional GFP-Type Cyclization and Unexpected Fragmentation Site in a Purple Chromoprotein fromAnemonia sulcata, asFP595†". Biochemistry. 43 (42): 13598–13603. doi:10.1021/bi0488247. ISSN 0006-2960. PMID 15491166.
  4. Chang, Hsin-Yang; Ko, Tzu-Ping; Chang, Yu-Ching; Huang, Kai-Fa; Lin, Cheng-Yung; Chou, Hong-Yun; Chiang, Cheng-Yi; Tsai, Huai-Jen (2019). "Crystal structure of the blue fluorescent protein with a Leu-Leu-Gly tri-peptide chromophore derived from the purple chromoprotein of Stichodactyla haddoni". International Journal of Biological Macromolecules. 130: 675–684. doi:10.1016/j.ijbiomac.2019.02.138. ISSN 0141-8130. PMID 30836182.


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