Cyanophycin, also known as CGP (cyanophycin granule poly

peptide Peptides are short chains of amino acids linked by peptide bonds. A polypeptide is a longer, continuous, unbranched peptide chain. Polypeptides that have a molecular mass of 10,000 Da or more are called proteins. Chains of fewer than twenty am ...

) or multi-L-arginyl-poly (L-aspartic acid), is a non-

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...

, non-ribosomally produced

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 a ...

polymer A polymer () is a chemical substance, substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeat unit, repeating subunits derived from one or more species of monomers. Due to their br ...

composed of an

aspartic acid Aspartic acid (symbol Asp or D; the ionic form is known as aspartate), is an α-amino acid that is used in the biosynthesis of proteins. The L-isomer of aspartic acid is one of the 22 proteinogenic amino acids, i.e., the building blocks of protei ...

backbone and

arginine Arginine is the amino acid with the formula (H2N)(HN)CN(H)(CH2)3CH(NH2)CO2H. The molecule features a guanidinium, guanidino group appended to a standard amino acid framework. At physiological pH, the carboxylic acid is deprotonated (−CO2−) a ...

side groups. Cyanophycin was first detected in 1887 by the Italian botanist

Antonino Borzì Antonino Borzì (20 August 1852, in Castroreale – 24 August 1921, in Lucca) was an Italian botanist. Life and career Antonino Borzì became a professor of botany at the University of Palermo in 1879 and at the University of Messina in 189 ...

and can be found in most

cyanobacteria Cyanobacteria ( ) are a group of autotrophic gram-negative bacteria that can obtain biological energy via oxygenic photosynthesis. The name "cyanobacteria" () refers to their bluish green (cyan) color, which forms the basis of cyanobacteri ...

and a few

heterotrophic A heterotroph (; ) is an organism that cannot produce its own food, instead taking nutrition from other sources of organic carbon, mainly plant or animal matter. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but ...

bacteria such as ''

Acinetobacter ''Acinetobacter'' is a genus of Gram-negative bacteria belonging to the wider class of Gammaproteobacteria. ''Acinetobacter'' species are oxidase-negative, exhibit twitching motility, and occur in pairs under magnification. They are important ...

'' sp. Cyanophycin is largely insoluble under physiological conditions and is accumulated in the form of granules in the

cytoplasm The cytoplasm describes all the material within a eukaryotic or prokaryotic cell, enclosed by the cell membrane, including the organelles and excluding the nucleus in eukaryotic cells. The material inside the nucleus of a eukaryotic cell a ...

during phosphate or sulfur starvation, generally in the early and mid-stationary phase. It is used as a nitrogen- and possibly carbon-storage compound and also serves as a dynamic buffer for fixed nitrogen in cyanobacterial

heterocysts Heterocysts or heterocytes are specialized nitrogen-fixing cells formed during nitrogen starvation by some filamentous cyanobacteria, such as ''Nostoc'', ''Cylindrospermum'', and '' Anabaena''. They fix nitrogen from dinitrogen (N2) in the air ...

. Nitrogen and carbon are mobilized from cyanophycin by intracellular cyanophycinase in the form of aspartate-arginine

dipeptide A dipeptide is an organic compound derived from two amino acids. The constituent amino acids can be the same or different. When different, two isomers of the dipeptide are possible, depending on the sequence. Several dipeptides are physiological ...

s. Cyanophycin is synthesized from arginine and aspartate in an ATP-dependent reaction catalyzed by a single

enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

, cyanophycin synthetase. Cyanophycin is of potential interest to

biotechnology Biotechnology is a multidisciplinary field that involves the integration of natural sciences and Engineering Science, engineering sciences in order to achieve the application of organisms and parts thereof for products and services. Specialists ...

as a source of polyaspartic acid. Due to its unusual polyamphoteric character, cyanophycin is soluble in water under acidic (0.1 M HCl) and alkaline conditions. Heterologous expression of cyanophycin synthetase allows production of cyanophycin in a number of biotechnologically relevant bacteria such as ''

Escherichia coli ''Escherichia coli'' ( )Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. is a gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus '' Escherichia'' that is commonly fo ...

'' and '' Corynebacterium glutamicum''. Since insoluble forms of CGP are easily purified, most studies have overlooked the synthesis of CGP that is soluble at a neutral pH. To compare the two, insoluble CGP can be solubilized by only weak

acids An acid is a molecule or ion capable of either donating a proton (i.e. hydrogen cation, H+), known as a Brønsted–Lowry acid, or forming a covalent bond with an electron pair, known as a Lewis acid. The first category of acids are the ...

while soluble CGP can be separated with the process of

precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls from clouds due to gravitational pull. The main forms of precipitation include drizzle, rain, rain and snow mixed ("sleet" in Commonwe ...

by using

acetone Acetone (2-propanone or dimethyl ketone) is an organic compound with the chemical formula, formula . It is the simplest and smallest ketone (). It is a colorless, highly Volatile organic compound, volatile, and flammable liquid with a charact ...

ethanol Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound with the chemical formula . It is an Alcohol (chemistry), alcohol, with its formula also written as , or EtOH, where Et is the ps ...

. In 2014, an experiment by Steinbüchel and Wiefel determined that the amount of

lysine Lysine (symbol Lys or K) is an α-amino acid that is a precursor to many proteins. Lysine contains an α-amino group (which is in the protonated form when the lysine is dissolved in water at physiological pH), an α-carboxylic acid group ( ...

residue can regulate the solubility of cyanophycin, with higher levels of lysine negatively correlating to the temperature needed to make the polymer soluble with aqueous solvents. It was concluded that insoluble and soluble CGP are not distinct polymers, since they originate from the same polymer mixture, but are instead classified as mixes of cyanophycin mixtures with varying concentrations of lysine residues. The ability of lysine to partially replace the arginine side chain encouraged research of CGP variants with amino acids such as

ornithine Ornithine is a non-proteinogenic α-amino acid that plays a role in the urea cycle. It is not incorporated into proteins during translation. Ornithine is abnormally accumulated in the body in ornithine transcarbamylase deficiency, a disorder of th ...

and

citrulline The organic compound citrulline is an α-amino acid. Its name is derived from '' citrullus'', the Latin word for watermelon. Although named and described by gastroenterologists since the late 19th century, it was first isolated from watermelon in ...

. Lysine, ornithine and citrulline all have an

affinity Affinity may refer to: Commerce, finance and law * Affinity (law), kinship by marriage * Affinity analysis, a market research and business management technique * Affinity Credit Union, a Saskatchewan-based credit union * Affinity Equity Pa ...

for cyanophycin synthase (L-aspartate-adding) enzyme CphA. Wiefel, Bröker and Steinbüchel conducted an experiment demonstrating that citrulline-rich cyanophycin can be produced through the introduction of a citrulline-producing strain. It was also determined that insoluble CGP only exhibited minuscule concentrations of citrulline while soluble CGP was able to produce a high concentration of citrulline. This trend is also similar for ornithine.

References

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