Cyanophycin, also known as CGP (cyanophycin

granule A granule is a large particle or grain. It can refer to: * Granule (cell biology), any of several submicroscopic structures, some with explicable origins, others noted only as cell type-specific features of unknown function ** Azurophilic granul ...

poly

peptide Peptides (, ) are short chains of amino acids linked by peptide bonds. Long chains of amino acids are called proteins. Chains of fewer than twenty amino acids are called oligopeptides, and include dipeptides, tripeptides, and tetrapeptides. ...

) 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 residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respon ...

, non-ribosomally produced

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha ...

polymer A polymer (; Greek ''poly-'', "many" + '' -mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic and ...

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. Like all other amino acids, it contains an amino group and a carboxylic acid. Its α-amino group is in the pr ...

backbone and

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

side groups. Cyanophycin was first detected in 1887 by the Italian botanist '' Antonino Borzì'' and can be found in most cyanobacteria 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 importan ...

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

cytoplasm In cell biology, the cytoplasm is all of the material within a eukaryotic cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. ...

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 punctiforme'', ''Cylindrospermum stagnale'', and ''Anabaena sphaerica''. They fix nitrogen fro ...

. 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 physiologicall ...

s. Cyanophycin is synthesized from arginine and aspartate in an

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-dependent reaction

catalyzed Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recycl ...

by a single

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different molecule ...

, cyanophycin synthetase. Cyanophycin is of potential interest to

biotechnology Biotechnology is the integration of natural sciences and engineering sciences in order to achieve the application of organisms, cells, parts thereof and molecular analogues for products and services. The term ''biotechnology'' was first used b ...

as a source of

polyaspartic acid Polyaspartic acid (PASA) is a biodegradable, water-soluble condensation polymer based on the amino acid aspartic acid. It is a biodegradable replacement for water softeners and related applications. PASA can be chemically crosslinked with a wide ...

. 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. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus '' Esc ...

'' 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 In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a ...

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 under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hai ...

by using

acetone Acetone (2-propanone or dimethyl ketone), is an organic compound with the formula . It is the simplest and smallest ketone (). It is a colorless, highly volatile and flammable liquid with a characteristic pungent odour. Acetone is miscible wi ...

ethanol Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an alcohol with the chemical formula . Its formula can be also written as or (an ethyl group linked to a h ...

. 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. It contains an α-amino group (which is in the protonated form under biological conditions), an α-carboxylic acid group (which is in the deprotonated &minu ...

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 amino acid that plays a role in the urea cycle. Ornithine is abnormally accumulated in the body in ornithine transcarbamylase deficiency. The radical is ornithyl. Role in urea cycle L-Ornithine is one of the prod ...

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 1 ...

. Lysine, ornithine and citrulline all have an

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for

cyanophycin synthase (L-aspartate-adding) Cyanophycin synthase (L-aspartate-adding) (, ''CphA'', ''CphA1'', ''CphA2'', ''cyanophycin synthetase'', ''multi-L-arginyl-poly-L-aspartate synthase'') is an enzyme with systematic name ''cyanophycin:L-aspartate ligase (ADP-forming)''. This enz ...

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

Peptides {{Biochem-stub