Chromoprotein

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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]

14 chromoproteins were engineered to be expressed in E. coli for synthetic biology. [5] However, chromoproteins bring high toxicities to their E. coli hosts, resulting in the loss of colors. mRFP1, the monomeric red fluorescent protein, [6] which also displays distinguishable color under ambient light, was found to be less toxic. [7] Color-changing mutagenesis on amino acids 64–65 of the mRFP1 fluorophore was done to acquire different colors.

Related Research Articles

<span class="mw-page-title-main">Cytochrome</span> Redox-active proteins containing a heme with a Fe atom as a cofactor

Cytochromes are redox-active proteins containing a heme, with a central iron (Fe) atom at its core, as a cofactor. They are involved in the electron transport chain and redox catalysis. They are classified according to the type of heme and its mode of binding. Four varieties are recognized by the International Union of Biochemistry and Molecular Biology (IUBMB), cytochromes a, cytochromes b, cytochromes c and cytochrome d.

<span class="mw-page-title-main">Green fluorescent protein</span> Protein that exhibits bright green fluorescence when exposed to ultraviolet light

The green fluorescent protein (GFP) is a protein that exhibits green fluorescence when exposed to light in the blue to ultraviolet range. The label GFP traditionally refers to the protein first isolated from the jellyfish Aequorea victoria and is sometimes called avGFP. However, GFPs have been found in other organisms including corals, sea anemones, zoanithids, copepods and lancelets.

<span class="mw-page-title-main">Fluorescent tag</span>

In molecular biology and biotechnology, a fluorescent tag, also known as a fluorescent label or fluorescent probe, is a molecule that is attached chemically to aid in the detection of a biomolecule such as a protein, antibody, or amino acid. Generally, fluorescent tagging, or labeling, uses a reactive derivative of a fluorescent molecule known as a fluorophore. The fluorophore selectively binds to a specific region or functional group on the target molecule and can be attached chemically or biologically. Various labeling techniques such as enzymatic labeling, protein labeling, and genetic labeling are widely utilized. Ethidium bromide, fluorescein and green fluorescent protein are common tags. The most commonly labelled molecules are antibodies, proteins, amino acids and peptides which are then used as specific probes for detection of a particular target.

A prosthetic group is the non-amino acid component that is part of the structure of the heteroproteins or conjugated proteins, being tightly linked to the apoprotein.

<span class="mw-page-title-main">Fluorophore</span> Agents that emit light after excitation by light

A fluorophore is a fluorescent chemical compound that can re-emit light upon light excitation. Fluorophores typically contain several combined aromatic groups, or planar or cyclic molecules with several π bonds.

<span class="mw-page-title-main">Phytochrome</span> Protein used by plants, bacteria and fungi to detect light

Phytochromes are a class of photoreceptor proteins found in plants, bacteria and fungi. They respond to light in the red and far-red regions of the visible spectrum and can be classed as either Type I, which are activated by far-red light, or Type II that are activated by red light. Recent advances have suggested that phytochromes also act as temperature sensors, as warmer temperatures enhance their de-activation. All of these factors contribute to the plant's ability to germinate.

<span class="mw-page-title-main">Biliverdin</span> Chemical compound

Biliverdin is a green tetrapyrrolic bile pigment, and is a product of heme catabolism. It is the pigment responsible for a greenish color sometimes seen in bruises.

<span class="mw-page-title-main">Phycocyanin</span> Protein complexes in algae

Phycocyanin is a pigment-protein complex from the light-harvesting phycobiliprotein family, along with allophycocyanin and phycoerythrin. It is an accessory pigment to chlorophyll. All phycobiliproteins are water-soluble, so they cannot exist within the membrane like carotenoids can. Instead, phycobiliproteins aggregate to form clusters that adhere to the membrane called phycobilisomes. Phycocyanin is a characteristic light blue color, absorbing orange and red light, particularly near 620 nm, and emits fluorescence at about 650 nm. Allophycocyanin absorbs and emits at longer wavelengths than phycocyanin C or phycocyanin R. Phycocyanins are found in cyanobacteria. Phycobiliproteins have fluorescent properties that are used in immunoassay kits. Phycocyanin is from the Greek phyco meaning “algae” and cyanin is from the English word “cyan", which conventionally means a shade of blue-green and is derived from the Greek “kyanos" which means a somewhat different color: "dark blue". The product phycocyanin, produced by Aphanizomenon flos-aquae and Spirulina, is for example used in the food and beverage industry as the natural coloring agent 'Lina Blue' or 'EXBERRY Shade Blue' and is found in sweets and ice cream. In addition, fluorescence detection of phycocyanin pigments in water samples is a useful method to monitor cyanobacteria biomass.

<span class="mw-page-title-main">Conjugated protein</span> Protein that contains a non-peptide component

A conjugated protein is a protein that functions in interaction with other (non-polypeptide) chemical groups attached by covalent bonding or weak interactions.

<span class="mw-page-title-main">Yellow fluorescent protein</span> Genetic mutant of green fluorescent protein

Yellow fluorescent protein (YFP) is a genetic mutant of green fluorescent protein (GFP) originally derived from the jellyfish Aequorea victoria. Its excitation peak is 513 nm and its emission peak is 527 nm. Like the parent GFP, YFP is a useful tool in cell and molecular biology because the excitation and emission peaks of YFP are distinguishable from GFP which allows for the study of multiple processes/proteins within the same experiment.

<span class="mw-page-title-main">Horseradish peroxidase</span> Chemical compound and enzyme

The enzyme horseradish peroxidase (HRP), found in the roots of horseradish, is used extensively in biochemistry applications. It is a metalloenzyme with many isoforms, of which the most studied type is C. It catalyzes the oxidation of various organic substrates by hydrogen peroxide.

Photoreceptor proteins are light-sensitive proteins involved in the sensing and response to light in a variety of organisms. Some examples are rhodopsin in the photoreceptor cells of the vertebrate retina, phytochrome in plants, and bacteriorhodopsin and bacteriophytochromes in some bacteria. They mediate light responses as varied as visual perception, phototropism and phototaxis, as well as responses to light-dark cycles such as circadian rhythm and other photoperiodisms including control of flowering times in plants and mating seasons in animals.

<span class="mw-page-title-main">Roger Y. Tsien</span> American biochemist and Nobel laureate (1952–2016)

Roger Yonchien Tsien was an American biochemist. He was a professor of chemistry and biochemistry at the University of California, San Diego and was awarded the Nobel Prize in Chemistry in 2008 for his discovery and development of the green fluorescent protein, in collaboration with organic chemist Osamu Shimomura and neurobiologist Martin Chalfie. Tsien was also a pioneer of calcium imaging.

Douglas C. Prasher is an American molecular biologist. He is known for his work to clone and sequence the genes for the photoprotein aequorin and green fluorescent protein (GFP) and for his proposal to use GFP as a tracer molecule. He communicated his pioneering work to Martin Chalfie and Roger Y. Tsien, but by 1991 he was unable to obtain further research funding, and left academia. Eventually, he had to abandon science. Chalfie and Tsien were awarded the 2008 Nobel Prize in Chemistry for work that they publicly acknowledged was substantially based on Prasher's work; through their efforts and those of others, he returned to scientific research in June 2010.

EosFP is a photoactivatable green to red fluorescent protein. Its green fluorescence (516 nm) switches to red (581 nm) upon UV irradiation of ~390 nm due to a photo-induced modification resulting from a break in the peptide backbone near the chromophore. Eos was first discovered as a tetrameric protein in the stony coral Lobophyllia hemprichii. Like other fluorescent proteins, Eos allows for applications such as the tracking of fusion proteins, multicolour labelling and tracking of cell movement. Several variants of Eos have been engineered for use in specific study systems including mEos2, mEos4 and CaMPARI.

mCherry is a member of the mFruits family of monomeric red fluorescent proteins (mRFPs). As a RFP, mCherry was derived from DsRed of Discosoma sea anemones unlike green fluorescent proteins (GFPs) which are often derived from Aequorea victoria jellyfish. Fluorescent proteins are used to tag components in the cell, so they can be studied using fluorescence spectroscopy and fluorescence microscopy. mCherry absorbs light between 540-590 nm and emits light in the range of 550-650 nm. mCherry belongs to the group of fluorescent protein chromophores used as instruments to visualize genes and analyze their functions in experiments. Genome editing has been improved greatly through the precise insertion of these fluorescent protein tags into the genetic material of many diverse organisms. Most comparisons between the brightness and photostability of different fluorescent proteins have been made in vitro, removed from biological variables that affect protein performance in cells or organisms. It is hard to perfectly simulate cellular environments in vitro, and the difference in environment could have an effect on the brightness and photostability.

<span class="mw-page-title-main">FMN-binding fluorescent protein</span>

A FMN-binding fluorescent protein (FbFP), also known as a LOV-based fluorescent protein, is a small, oxygen-independent fluorescent protein that binds flavin mononucleotide (FMN) as a chromophore.

<span class="mw-page-title-main">SmURFP</span>

Small ultra red fluorescent protein (smURFP) is a class of far-red fluorescent protein evolved from a cyanobacterial phycobiliprotein, α-allophycocyanin. Native α-allophycocyanin requires an exogenous protein, known as a lyase, to attach the chromophore, phycocyanobilin. Phycocyanobilin is not present in mammalian cells. smURFP was evolved to covalently attach phycocyanobilin without a lyase and fluoresce, covalently attach biliverdin and fluoresce, blue-shift fluorescence to match the organic fluorophore, Cy5, and not inhibit E. coli growth. smURFP was found after 12 rounds of random mutagenesis and manually screening 10,000,000 bacterial colonies.

<span class="mw-page-title-main">Red fluorescent protein</span>

Red fluorescent protein (RFP) is a fluorophore that fluoresces red-orange when excited. Several variants have been developed using directed mutagenesis. The original was isolated from Discosoma, and named DsRed. Others are now available that fluoresce orange, red, and far-red.

<span class="mw-page-title-main">Biliprotein</span>

Biliproteins are pigment protein compounds that are located in photosynthesising organisms such as algae and certain insects. They refer to any protein that contains a bilin chromophore. In plants and algae, the main function of biliproteins is to make the process of light accumulation required for photosynthesis more efficient; while in insects they play a role in growth and development. Some of their properties: including light-receptivity, light-harvesting and fluorescence have made them suitable for applications in bioimaging and as indicators; while other properties such as anti-oxidation, anti-aging and anti-inflammation in phycobiliproteins have given them potential for use in medicine, cosmetics and food technology. While research on biliproteins dates back as far as 1950, it was hindered due to issues regarding biliprotein structure, lack of methods available for isolating individual biliprotein components, as well as limited information on lyase reactions . Research on biliproteins has also been primarily focused on phycobiliproteins; but advances in technology and methodology, along with the discovery of different types of lyases, has renewed interest in biliprotein research, allowing new opportunities for investigating biliprotein processes such as assembly/disassembly and protein folding.

References

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