An Overview of Hemocyanin

Hemocyanin, also known as hemocyanin, is a multifunctional protein that was previously called respiratory protein, but recent studies have shown that the protein is involved in energy storage, maintenance of osmotic pressure and regulation of the molting process.

Introduction of Hemocyanin

Hemocyanin is a free blue respiratory pigment found in the haemolymph of certain mollusks, arthropods (spiders and beetles). Hemocyanin contains two copper ions directly linked to the polypeptide chain, and iron-containing hemoglobin similar to its easy oxygen, but also easy to dissociate with oxygen, is the only known with oxygen reversible copper protein binding, oxidation was Green, restore when white. The molecular weight of 450 000 ~ 130 000. Arthropod hemocyanin A polypeptide chain with a molecular oxygen binding, copper 0.17%; mollusk hemocyanin a polypeptide chain is combined with 6 molecular oxygen, copper 0.025%. Copper binds directly to the protein in a bivalent form. Hemocyanin has a variety of catalytic, especially after denaturation, under certain conditions with polyphenol oxidase, catalase and lipoxygenase activity.

In some invertebrates, the blood of most animals is free of hemoglobin, such as molluscs (cephalopods and petunias) and arthropods (limulus of the shrimp, crab and limulus) Also known as hemocyanin). The hemocyanin molecule is composed of Cu2+ and a peptide chain of about 200 or more amino acids. Like hemoglobin, the color of the respiratory pigment is related to its state. It is blue in oxygen and in the state. In the non-oxygen state Colorless or white.

Hemocyanin is a copper-containing respiratory protein in the hemolymph of arthropods and molluscs. The deoxidized state is colorless and the bound oxygen state is blue. Molecular mass is generally 50ku~75ku, composed of seven or eight functional units of cylindrical structure. The number of subunits that make up the hemocyanin is high, and each subunit contains two Cu (Ⅰ) ions. Different proteins contain different numbers of subunits, some of the molecular weight of hemocyanin up to 9×103ku. It is a cylindrical molecule with 10~20 subunits. Each subunit (molecular weight 350ku~450ku) has 7~8 functional units (oxygen molecule binding site). Arthropod hemocyanin is composed of hexamer or hexamers and has a molecular mass of about 3.5 × 103ku. Each subunit (7.5ku) contains an oxygenated center. The main biological function of hemocyanin and oxygen in the body related to it with hemoglobins and earthworm hemerythreins and known as the animal in the three respiratory protein. However, recent studies have shown that hemocyanin is a multifunctional protein, it not only has oxygen function, but also with the energy storage, osmotic pressure maintenance and molt process regulation. Particular attention to the academic community, the hemocyanin also has phenoloxidase activity and antibacterial function, is considered arthropods and mollusks in an important immune molecules.

Structural characteristics of Hemocyanin

Hemocyanin is a copper-containing respiratory protein in the haemolymph of shrimp. Each oxygen-binding site has two copper atoms, and its oxygen binding site is linked to another copper ion binding protein, the oxygen-binding site of phenoloxidase Of the structure has a high similarity. Hemocyanin in the deoxidized state is colorless, combined with oxygen blue.

The structure characteristics of hemocyanin in horseshoe crab were studied by polyacrylamide gel electrophoresis (PAGE) and electron microscopy. The results showed that purified hemocyanin by Sephadex G-100 appeared in PAGE electrophoresis. 4 bands. Purified hemocyanin was further purified by DEAE-32 chromatography to obtain 5 elution peaks. Each peak was identified by PAGE. Electron microscopy revealed that the hemocyanin molecules were circular, Pentagonal, cross-shaped and bow-shaped configuration and other dissociation with the middle of the configuration at the same time.

In the arthropods, clathrates, crustaceans, polyps and spiders contain hemocyanin, but the largest group of insects, although not the presence of hemocyanin, contains homologs of hemocyanin, Hexamer). Hexavalentin is divided into two groups rich in aromatic amino acids and methyl-sulfur-rich amino acids. Arthropod-type hemocyanin has also been found in the onychophora, a close relative of arthropods. Arthropod-type hemocyanin has a four-stage structure and a tertiary structure. Hemocyanin has a tertiary structure with a molecular mass of about 75ku, in which the second domain is the alpha helix, the chelating pair of Cu+, the binding of one O2, the third domain below, Containing Ca ion, function is unknown.

Arthropod hemocyanin at least has differentiated into: ① phenoloxidase (prophenoloxidase); ② insect hexapeptide (hexamer), does not chelate Cu +, for the storage protein; ③ crustaceans pseudochrome protein (pseudohemocyanin or cryptocyanin ), But also for the storage protein; ④bipolar hexapeptide receptor. The molecular phylogenetic analysis, they together with the hemocyanin protein, together to build the arthropod hemocyanin gene superfamily.

The function of hemocyanin

Oxygen carrier function: Hemocyanin is a protein with univalent copper ions as its cofactor. The physiological function of hemocyanin is oxygen. Oxyhemoglobin copper is Cu (Ⅱ) and blue, in the vicinity of 347 nm absorption peak. Deoxyhemoglobin is colorless. X-ray diffraction technology has greatly increased the understanding of hemocyanin. In 1978, Simmons M G and Wilson L J synthesized Cu (I) complexes with imidazole as ligand, which can reversibly carry oxygen at room temperature, either in solution or in solid state.

Antiviral effect: Hemocyanin has a nonspecific antiviral effect. Hemocyanin is a potential viral inhibitor at low concentrations, but hemocyanin does not completely inhibit viral replication.

Agglutination: In recent years, studies at home and abroad have confirmed that limpet hemocyanin may be evolved by phenol oxidase. The activation of phenoloxidase cascade system is closely related to the clotting mechanism of thromboplastin in crustaceans. It has been found that hemocyanin also has an agglutinating activity. These results suggest that hemocyanin, phenoloxidase and thromboplastin may be evolved from the same protein, while the multifunctional molecule of hemocyanin retains all of their immunological functions.

Antibacterial effect: Antimicrobial peptides produced by the cleavage of hemocyanin are associated with the immune response to shrimp. When the shrimp is infected, the concentration of the active peptide in the C-terminal sequence of this hemocyanin increases, indicating that lysis of the hemocyanin is caused by the biological signal. Lee S Y, etc. from freshwater crayfish plasma obtained by a 16 amino acid composition of the antimicrobial peptide, can inhibit G+ and G-bacteria growth. This antimicrobial peptide is produced by proteolytic cleavage of hemocyanin under acidic conditions. Injection of lipopolysaccharide and dextran can promote the production and release of this peptide. This suggests that antimicrobial peptides can be induced, released and activated, and thus play a role in the body's immune defense.