Hemocyanin

Last updated
Hemocyanin, copper containing domain
Hemocyanin2.jpg
Single oxygenated functional unit from the hemocyanin of an octopus
Identifiers
SymbolHemocyanin_M
Pfam PF00372
InterPro IPR000896
PROSITE PDOC00184
SCOP2 1lla / SCOPe / SUPFAM
Available protein structures:
Pfam   structures / ECOD  
PDB RCSB PDB; PDBe; PDBj
PDBsum structure summary
PDB 1oxy :110-373 1nol :110-373 1lla :110-373

1ll1 :110-373 1hc1 A:136-393 1hcy D:136-393 1hc6 B:136-393 1hc4 C:136-393 1hc3 C:136-393

Contents

1hc5 C:136-393 1hc2 C:136-393
Hemocyanin, all-alpha domain
PDB 1hcy EBI.jpg
Crystal structure of hexameric haemocyanin from Panulirus interruptus refined at 3.2 angstroms resolution
Identifiers
SymbolHemocyanin_N
Pfam PF03722
InterPro IPR005204
PROSITE PDOC00184
SCOP2 1lla / SCOPe / SUPFAM
Available protein structures:
Pfam   structures / ECOD  
PDB RCSB PDB; PDBe; PDBj
PDBsum structure summary
Hemocyanin, ig-like domain
PDB 1oxy EBI.jpg
crystallographic analysis of oxygenated and deoxygenated states of arthropod hemocyanin shows unusual differences
Identifiers
SymbolHemocyanin_C
Pfam PF03723
InterPro IPR005203
PROSITE PDOC00184
SCOP2 1lla / SCOPe / SUPFAM
Available protein structures:
Pfam   structures / ECOD  
PDB RCSB PDB; PDBe; PDBj
PDBsum structure summary

Hemocyanins (also spelled haemocyanins and abbreviated Hc) are proteins that transport oxygen throughout the bodies of some invertebrate animals. These metalloproteins contain two copper atoms that reversibly bind a single oxygen molecule (O2). They are second only to hemoglobin in frequency of use as an oxygen transport molecule. Unlike the hemoglobin in red blood cells found in vertebrates, hemocyanins are not confined in blood cells, but are instead suspended directly in the hemolymph. Oxygenation causes a color change between the colorless Cu(I) deoxygenated form and the blue Cu(II) oxygenated form. [1]

Species distribution

Hemocyanin was first discovered in Octopus vulgaris by Leon Fredericq in 1878. The presence of copper in molluscs was detected even earlier by Bartolomeo Bizio in 1833. [2] Hemocyanins are found in the Mollusca and Arthropoda, including cephalopods and crustaceans, and utilized by some land arthropods such as the tarantula Eurypelma californicum , [3] the emperor scorpion, [4] and the centipede Scutigera coleoptrata . Also, larval storage proteins in many insects appear to be derived from hemocyanins. [5]

The hemocyanin superfamily

The arthropod hemocyanin superfamily is composed of phenoloxidases, hexamerins, pseudohemocyanins or cryptocyanins, and (dipteran) hexamerin receptors. [6]

Phenoloxidase are copper containing tyrosinases. These proteins are involved in the process of sclerotization of arthropod cuticle, in wound healing, and humoral immune defense. Phenoloxidase is synthesized by zymogens and are activated by cleaving an N-terminal peptide. [7]

Hexamerins are storage proteins commonly found in insects. These proteins are synthesized by the larval fat body and are associated with molting cycles or nutritional conditions. [8]

Pseudohemocyanin and cryptocyanins genetic sequences are closely related to hemocyanins in crustaceans. These proteins have a similar structure and function, but lack the copper binding sites. [9]

The evolutionary changes within the phylogeny of the hemocyanin superfamily are closely related to the emergence of these different proteins in various species. The understanding of proteins within this superfamily would not be well understood without the extensive studies of hemocyanin in arthropods. [10]

Structure and mechanism

Although the respiratory function of hemocyanin is similar to that of hemoglobin, there are a significant number of differences in its molecular structure and mechanism. Whereas hemoglobin carries its iron atoms in porphyrin rings (heme groups), the copper atoms of hemocyanin are bound as prosthetic groups coordinated by histidine residues. Each hemocyanin monomer holds a pair of copper(I) cations in place via interactions with the imidazole rings of six histidine residues. [11] It has been noted that species using hemocyanin for oxygen transportation include crustaceans living in cold environments with low oxygen pressure. Under these circumstances hemoglobin oxygen transportation is less efficient than hemocyanin oxygen transportation. [12] Nevertheless, there are also terrestrial arthropods using hemocyanin, notably spiders and scorpions, that live in warm climates. The molecule is conformationally stable and fully functioning at temperatures up to 90 degrees C. [13]

Most hemocyanins bind with oxygen non-cooperatively and are roughly one-fourth as efficient as hemoglobin at transporting oxygen per amount of blood. Hemoglobin binds oxygen cooperatively due to steric conformation changes in the protein complex, which increases hemoglobin's affinity for oxygen when partially oxygenated. In some hemocyanins of horseshoe crabs and some other species of arthropods, cooperative binding is observed, with Hill coefficients of 1.6–3.0. Hill coefficients vary depending on species and laboratory measurement settings. Hemoglobin, for comparison, has a Hill coefficient of usually 2.8–3.0. In these cases of cooperative binding hemocyanin was arranged in protein sub-complexes of 6 subunits (hexamer) each with one oxygen binding site; binding of oxygen on one unit in the complex would increase the affinity of the neighboring units. Each hexamer complex was arranged together to form a larger complex of dozens of hexamers. In one study, cooperative binding was found to be dependent on hexamers being arranged together in the larger complex, suggesting cooperative binding between hexamers. Hemocyanin oxygen-binding profile is also affected by dissolved salt ion levels and pH. [14]

Hemocyanin is made of many individual subunit proteins, each of which contains two copper atoms and can bind one oxygen molecule (O2). Each subunit weighs about 75 kilodaltons (kDa). Subunits may be arranged in dimers or hexamers depending on species; the dimer or hexamer complex is likewise arranged in chains or clusters with weights exceeding 1500 kDa. The subunits are usually homogeneous, or heterogeneous with two variant subunit types. Because of the large size of hemocyanin, it is usually found free-floating in the blood, unlike hemoglobin. [15]

The 3.8 MDa structure of molluscan Japanese flying squid hemocyanin. It is a homodecamer of five dimers arranged into a 31 nm diameter cylinder. Each monomer has a string of eight individual subunits each with a Cu2O2 binding site. PDB: 4YD9 Molluscan hemocyanin (4YD9).png
The 3.8 MDa structure of molluscan Japanese flying squid hemocyanin. It is a homodecamer of five dimers arranged into a 31 nm diameter cylinder. Each monomer has a string of eight individual subunits each with a Cu2O2 binding site. PDB: 4YD9 ​

Hexamers are characteristic of arthropod hemocyanins. [17] A hemocyanin of the tarantula Eurypelma californicum [3] is made up of 4 hexamers or 24 peptide chains. A hemocyanin from the house centipede Scutigera coleoptrata [18] is made up of 6 hexamers or 36 chains. Horseshoe crabs have an 8-hexamer (i. e. 48-chain) hemocyanin. Simple hexamers are found in the spiny lobster Panulirus interruptus and the isopod Bathynomus giganteus. [17] Peptide chains in crustaceans are about 660 amino acid residues long, and in chelicerates they are about 625. In the large complexes there is a variety of variant chains, all about the same length; pure components do not usually self-assemble.[ citation needed ]

Catalytic activity

A hemocyanin active site in the absence of O2 (each Cu center is a cation, charges not shown). Deoxyhemocyanin full.png
A hemocyanin active site in the absence of O2 (each Cu center is a cation, charges not shown).
O2-bound form of a hemocyanin active site (the Cu2 center is a dication, charge not shown). Oxyhemocyanin full.png
O2-bound form of a hemocyanin active site (the Cu2 center is a dication, charge not shown).

Hemocyanin is homologous to the phenol oxidases (e.g. tyrosinase) since both proteins have histidine residues, called "type 3" copper-binding coordination centers, as do the enzymes tyrosinase and catechol oxidase. [19] In both cases inactive precursors to the enzymes (also called zymogens or proenzymes) must be activated first. This is done by removing the amino acid that blocks the entrance channel to the active site when the proenzyme is not active. There is currently no other known modifications necessary to activate the proenzyme and enable catalytic activity. Conformational differences determine the type of catalytic activity that the hemocyanin is able to perform. [20] Hemocyanin also exhibits phenol oxidase activity, but with slowed kinetics from greater steric bulk at the active site. Partial denaturation actually improves hemocyanin's phenol oxidase activity by providing greater access to the active site. [1] [19]

Spectral properties

The underside of the carapace of a red rock crab (Cancer productus). The purple coloring is caused by hemocyanin. Hemocyanin Example.jpg
The underside of the carapace of a red rock crab ( Cancer productus ). The purple coloring is caused by hemocyanin.

Spectroscopy of oxyhemocyanin shows several salient features: [21]

  1. Resonance Raman spectroscopy shows that O
    2     is bound in a symmetric environment (ν(O-O) is not IR-allowed).
  2. OxyHc is EPR-silent indicating the absence of unpaired electrons
  3. Infrared spectroscopy shows ν(O-O) of 755 cm−1

Much work has been devoted to preparing synthetic analogues of the active site of hemocyanin. [21] One such model, which features a pair of copper centers bridged side-on by peroxo ligand, shows ν(O-O) at 741 cm−1 and a UV-Vis spectrum with absorbances at 349 and 551 nm. Both of these measurements agree with the experimental observations for oxyHc. [22] The Cu-Cu separation in the model complex is 3.56 Å, that of oxyhemocyanin is ca. 3.6 Å (deoxyHc: ca. 4.6 Å). [22] [23] [24]

Anticancer effects

The hemocyanin found in the blood of the Chilean abalone, Concholepas concholepas , has immunotherapeutic effects against bladder cancer in murine models. Mice primed with C. concholepas before implantation of bladder tumor (MBT-2) cells. Mice treated with C. concholepas hemocyanin showed antitumor effects: prolonged survival, decreased tumor growth and incidence, and lack of toxic effects and may have a potential use in future immunotherapy for superficial bladder cancer. [25]

Keyhole limpet hemocyanin (KLH) is an immune stimulant derived from circulating glycoproteins of the marine mollusk Megathura crenulata. KLH has been shown to be a significant treatment against the proliferations of breast cancer, pancreas cancer, and prostate cancer cells when delivered in vitro. Keyhole limpet hemocyanin inhibits growth of human Barrett's esophageal cancer through both apoptic and nonapoptic mechanisms of cell death. [26]

Case studies: environmental impact on hemocyanin levels

A 2003 study of the effect of culture conditions of blood metabolites and hemocyanin of the white shrimp Litopenaeus vannamei found that the levels of hemocyanin, oxyhemocyanin in particular, are affected by the diet. The study compared oxyhemocyanin levels in the blood of white shrimp housed in an indoor pond with a commercial diet with that of white shrimp housed in an outdoor pond with a more readily available protein source (natural live food) as well. Oxyhemocyanin and blood glucose levels were higher in shrimp housed in outdoor ponds. It was also found that blood metabolite levels tended to be lower in low activity level species, such as crabs, lobsters, and the indoor shrimp when compared to the outdoor shrimp. This correlation is possibly indicative of the morphological and physiological evolution of crustaceans. The levels of these blood proteins and metabolites appear to be dependent on energetic demands and availability of those energy sources. [27]

See also

Related Research Articles

<span class="mw-page-title-main">Hemoglobin</span> Metalloprotein that binds with oxygen

Hemoglobin is a protein containing iron that facilitates the transport of oxygen in red blood cells. Almost all vertebrates contain hemoglobin, with the exception of the fish family Channichthyidae. Hemoglobin in the blood carries oxygen from the respiratory organs to the other tissues of the body, where it releases the oxygen to enable aerobic respiration which powers the animal's metabolism. A healthy human has 12 to 20 grams of hemoglobin in every 100 mL of blood. Hemoglobin is a metalloprotein, a chromoprotein, and globulin.

<span class="mw-page-title-main">Myoglobin</span> Iron and oxygen-binding protein

Myoglobin is an iron- and oxygen-binding protein found in the cardiac and skeletal muscle tissue of vertebrates in general and in almost all mammals. Myoglobin is distantly related to hemoglobin. Compared to hemoglobin, myoglobin has a higher affinity for oxygen and does not have cooperative binding with oxygen like hemoglobin does. Myoglobin consists of non-polar amino acids at the core of the globulin, where the heme group is non-covalently bounded with the surrounding polypeptide of myoglobin. In humans, myoglobin is found in the bloodstream only after muscle injury.

<span class="mw-page-title-main">Hemoprotein</span> Protein containing a heme prosthetic group

A hemeprotein, or heme protein, is a protein that contains a heme prosthetic group. They are a very large class of metalloproteins. The heme group confers functionality, which can include oxygen carrying, oxygen reduction, electron transfer, and other processes. Heme is bound to the protein either covalently or noncovalently or both.

<span class="mw-page-title-main">Cytochrome c oxidase</span> Complex enzyme found in bacteria, archaea, and mitochondria of eukaryotes

The enzyme cytochrome c oxidase or Complex IV is a large transmembrane protein complex found in bacteria, archaea, and the mitochondria of eukaryotes.

<span class="mw-page-title-main">Hemerythrin</span> InterPro Family

Hemerythrin (also spelled haemerythrin; Ancient Greek: αἷμα, romanized: haîma, lit. 'blood', Ancient Greek: ἐρυθρός, romanized: erythrós, lit. 'red') is an oligomeric protein responsible for oxygen (O2) transport in the marine invertebrate phyla of sipunculids, priapulids, brachiopods, and in a single annelid worm genus, Magelona. Myohemerythrin is a monomeric O2-binding protein found in the muscles of marine invertebrates. Hemerythrin and myohemerythrin are essentially colorless when deoxygenated, but turn a violet-pink in the oxygenated state.

<span class="mw-page-title-main">Globin</span> Superfamily of oxygen-transporting globular proteins

The globins are a superfamily of heme-containing globular proteins, involved in binding and/or transporting oxygen. These proteins all incorporate the globin fold, a series of eight alpha helical segments. Two prominent members include myoglobin and hemoglobin. Both of these proteins reversibly bind oxygen via a heme prosthetic group. They are widely distributed in many organisms.

Cooperative binding occurs in molecular binding systems containing more than one type, or species, of molecule and in which one of the partners is not mono-valent and can bind more than one molecule of the other species. In general, molecular binding is an interaction between molecules that results in a stable physical association between those molecules.

<span class="mw-page-title-main">Metalloprotein</span> Protein that contains a metal ion cofactor

Metalloprotein is a generic term for a protein that contains a metal ion cofactor. A large proportion of all proteins are part of this category. For instance, at least 1000 human proteins contain zinc-binding protein domains although there may be up to 3000 human zinc metalloproteins.

<span class="mw-page-title-main">Hemolymph</span> Body fluid that circulates in the interior of an arthropod body

Hemolymph, or haemolymph, is a fluid, analogous to the blood in vertebrates, that circulates in the interior of the arthropod (invertebrate) body, remaining in direct contact with the animal's tissues. It is composed of a fluid plasma in which hemolymph cells called hemocytes are suspended. In addition to hemocytes, the plasma also contains many chemicals. It is the major tissue type of the open circulatory system characteristic of arthropods. In addition, some non-arthropods such as mollusks possess a hemolymphatic circulatory system.

<span class="mw-page-title-main">Fetal hemoglobin</span> Oxygen carrier protein in the human fetus

Fetal hemoglobin, or foetal haemoglobin is the main oxygen carrier protein in the human fetus. Hemoglobin F is found in fetal red blood cells, and is involved in transporting oxygen from the mother's bloodstream to organs and tissues in the fetus. It is produced at around 6 weeks of pregnancy and the levels remain high after birth until the baby is roughly 2–4 months old. Hemoglobin F has a different composition than adult forms of hemoglobin, allowing it to bind oxygen more strongly; this in turn enables the developing fetus to retrieve oxygen from the mother's bloodstream, which occurs through the placenta found in the mother's uterus.

<span class="mw-page-title-main">Vanabin</span> Family of vanadium-binding proteins

Vanabins are a group of vanadium-binding metalloproteins. Vanabins are found almost exclusively in the blood cells, or vanadocytes, of some tunicates, including the Ascidiacea. The vanabins extracted from tunicate vanadocytes are often called hemovanadins. These organisms are able to concentrate vanadium from the surrounding seawater, and vanabin proteins have been involved in collecting and accumulating this metal ion. At present there is no conclusive understanding of why these organisms collect vanadium.

A respiratory pigment is a metalloprotein that serves a variety of important functions, its main being O2 transport. Other functions performed include O2 storage, CO2 transport, and transportation of substances other than respiratory gases. There are four major classifications of respiratory pigment: hemoglobin, hemocyanin, erythrocruorin–chlorocruorin, and hemerythrin. The heme-containing globin is the most commonly-occurring respiratory pigment, occurring in at least 9 different phyla of animals.

<span class="mw-page-title-main">Tyrosinase</span> Enzyme for controlling the production of melanin

Tyrosinase is an oxidase that is the rate-limiting enzyme for controlling the production of melanin. The enzyme is mainly involved in two distinct reactions of melanin synthesis otherwise known as the Raper–Mason pathway. Firstly, the hydroxylation of a monophenol and secondly, the conversion of an o-diphenol to the corresponding o-quinone. o-Quinone undergoes several reactions to eventually form melanin. Tyrosinase is a copper-containing enzyme present in plant and animal tissues that catalyzes the production of melanin and other pigments from tyrosine by oxidation. It is found inside melanosomes which are synthesized in the skin melanocytes. In humans, the tyrosinase enzyme is encoded by the TYR gene.

Copper proteins are proteins that contain one or more copper ions as prosthetic groups. Copper proteins are found in all forms of air-breathing life. These proteins are usually associated with electron-transfer with or without the involvement of oxygen (O2). Some organisms even use copper proteins to carry oxygen instead of iron proteins. A prominent copper protein in humans is in cytochrome c oxidase (cco). This enzyme cco mediates the controlled combustion that produces ATP. Other copper proteins include some superoxide dismutases used in defense against free radicals, peptidyl-α-monooxygenase for the production of hormones, and tyrosinase, which affects skin pigmentation.

Catechol oxidase is a copper oxidase that contains a type 3 di-copper cofactor and catalyzes the oxidation of ortho-diphenols into ortho-quinones coupled with the reduction of molecular oxygen to water. It is present in a variety of species of plants and fungi including Ipomoea batatas and Camellia sinensis. Metalloenzymes with type 3 copper centers are characterized by their ability to reversibly bind dioxygen at ambient conditions. In plants, catechol oxidase plays a key role in enzymatic browning by catalyzing the oxidation of catechol to o-quinone in the presence of oxygen, which can rapidly polymerize to form the melanin that grants damaged fruits their dark brown coloration.

Iron-binding proteins are carrier proteins and metalloproteins that are important in iron metabolism and the immune response. Iron is required for life.

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

Neuroglobin is a member of the vertebrate globin family involved in cellular oxygen homeostasis and reactive oxygen/nitrogen scavenging. It is an intracellular hemoprotein expressed in the central and peripheral nervous system, cerebrospinal fluid, retina and endocrine tissues. Neuroglobin is a monomer that reversibly binds oxygen with an affinity higher than that of hemoglobin. It also increases oxygen availability to brain tissue and provides protection under hypoxic or ischemic conditions, potentially limiting brain damage. Neuroglobin were in the past found only in vertebrate neurons, but recently in 2013, were found in the neurons of unrelated protostomes, like photosynthetic acoel as well as radiata such as jellyfish. In addition to neurons, neuroglobin is present in astrocytes in certain pathologies of the rodent brain and in the physiological seal brain. This is thought to be due to convergent evolution. It is of ancient evolutionary origin, and is homologous to nerve globins of invertebrates. Recent research confirmed the presence of human neuroglobin protein in cerebrospinal fluid (CSF).

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

Erythrocruorin, and the similar chlorocruorin, are large oxygen-carrying hemeprotein complexes, which have a molecular mass greater than 3.5 million daltons. Both are sometimes called giant hemoglobin or hexagonal bilayer haemoglobin. They are found in many annelids and arthropods.

<span class="mw-page-title-main">Keyhole limpet hemocyanin</span>

Keyhole limpet hemocyanin (KLH) is a large, multisubunit, oxygen-carrying, metalloprotein that is found in the hemolymph of the giant keyhole limpet, Megathura crenulata, a species of keyhole limpet that lives off the coast of California, from Monterey Bay to Isla Asuncion off Baja California.

Dioxygen complexes are coordination compounds that contain O2 as a ligand. The study of these compounds is inspired by oxygen-carrying proteins such as myoglobin, hemoglobin, hemerythrin, and hemocyanin. Several transition metals form complexes with O2, and many of these complexes form reversibly. The binding of O2 is the first step in many important phenomena, such as cellular respiration, corrosion, and industrial chemistry. The first synthetic oxygen complex was demonstrated in 1938 with cobalt(II) complex reversibly bound O2.

References

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  24. ↑ Kodera M, Katayama K, Tachi Y, Kano K, Hirota S, Fujinami S, et al. (1999). "Crystal Structure and Reversible O2-Binding of a Room Temperature Stable μ-η2:η2-Peroxodicopper(II) Complex of a Sterically Hindered Hexapyridine Dinucleating Ligand". Journal of the American Chemical Society. 121 (47): 11006–7. doi:10.1021/ja992295q.
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  27. ↑ Pascual C, Gaxiola G, Rosas C (2003). "Blood metabolites and hemocyanin of the white shrimp, Litopenaeus vannamei: The effect of culture conditions and a comparison with other crustacean species". Marine Biology. 142 (4): 735–745. doi:10.1007/s00227-002-0995-2. S2CID   82961592.

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