Ceruloplasmin Explained

Ceruloplasmin (or caeruloplasmin) is a ferroxidase enzyme that in humans is encoded by the CP gene.^{[1] [2] [3]}

Ceruloplasmin is the major copper-carrying protein in the blood, and in addition plays a role in iron metabolism. It was first described in 1948.^[4] Another protein, hephaestin, is noted for its homology to ceruloplasmin, and also participates in iron and probably copper metabolism.

Function

Ceruloplasmin (CP) is an enzyme synthesized in the liver containing 6 atoms of copper in its structure.^[5] Ceruloplasmin carries more than 95% of the total copper in healthy human plasma.^[6] The rest is accounted for by macroglobulins. Ceruloplasmin exhibits a copper-dependent oxidase activity, which is associated with possible oxidation of Fe²⁺ (ferrous iron) into Fe³⁺ (ferric iron), therefore assisting in its transport in the plasma in association with transferrin, which can carry iron only in the ferric state.^[7] The molecular weight of human ceruloplasmin is reported to be 151kDa.

Despite extensive research, much is still unknown about the exact functions of CP, most of the functions are attributed to CP focus on the presence of the Cu centers. These include copper transport to deliver the Cu to extrahepatic tissues, amine oxidase activity that controls the level of biogenic amines in intestinal fluids and plasma, removal of oxygen and other free radicals from plasma, and the export of iron from cells for transport through transferrin.^[8]

Mutations have been known to disrupt the binding of copper to CP and will disrupt iron metabolism and cause an iron overload.

Ceruloplasmin is a relatively large enzyme (~10nm); the larger size prevents the bound copper from being lost in a person's urine during transport.

Active site structure

The multicopper active site of CP contains a type I (T1) mononuclear copper site and a trinuclear copper center ~ 12-13 Å away (see figure 2).  The tricopper center consists of two type III (T3) coppers and one type II (T2) copper ion.  The two T3 copper ions are bridged by a hydroxide ligand while another hydroxide ligand links the T2 copper ion to the protein.  The T1 center is bridged to the tricopper center by two histidine (His1020, His1022) residues and one Cys(1021) residue.  The substrate binds near the T1 center and is oxidized by the T1 Cu²⁺ ion forming the reduced Cu⁺ oxidation state.  The reduced T1 Cu⁺ then transfers the electron through the one Cys and two His bridging residues to the tricopper center.  After four electrons have been transferred from the substrates to the copper centers, an O₂ binds at the tricopper center and undergoes a four-electron reduction to form two molecules of water.^[9]

Regulation

A cis-regulatory element called the GAIT element is involved in the selective translational silencing of the Ceruloplasmin transcript.^[10] The silencing requires binding of a cytosolic inhibitor complex called IFN-gamma-activated inhibitor of translation (GAIT) to the GAIT element.^[11]

Clinical significance

Like any other plasma protein, levels drop in patients with hepatic disease due to reduced synthesizing capabilities.

Mechanisms of low ceruloplasmin levels:

• Gene expression genetically low (aceruloplasminemia)
• Copper levels are low in general
  • Malnutrition/trace metal deficiency in the food source
  • Zinc toxicity, due to induced copper deficiency
• Copper does not cross the intestinal barrier due to ATP7A deficiency (Menkes disease and Occipital horn syndrome)
• Delivery of copper into the lumen of the ER-Golgi network is absent in hepatocytes due to absent ATP7B (Wilson's disease)

Copper availability doesn't affect the translation of the nascent protein. However, the apoenzyme without copper is unstable. Apoceruloplasmin is largely degraded intracellularly in the hepatocyte and the small amount that is released has a short circulation half life of 5 hours as compared to the 5.5 days for the holo-ceruloplasmin.

Ceruloplasmin can be measured by means of a blood test;^[12] this can be done using immunoassays . The sample is spun and separated; it is stored around 4°C Celsius for three days. This test is to determine if there are signs of Wilson disease. Another test that can be done is a urine copper level test; this has been found to be less accurate than the blood test. A liver tissue test can be done as well.

Mutations in the ceruloplasmin gene (CP), which are very rare, can lead to the genetic disease aceruloplasminemia, characterized by hyperferritinemia with iron overload. In the brain, this iron overload may lead to characteristic neurologic signs and symptoms, such as cerebellar ataxia, progressive dementia, and extrapyramidal signs. Excess iron may also deposit in the liver, pancreas, and retina, leading to cirrhosis, endocrine abnormalities, and loss of vision, respectively.

Deficiency

Lower-than-normal ceruloplasmin levels may indicate the following:

• Wilson disease (a rare [UK incidence 2/100,000] copper storage disease).^[13]
• Menkes disease (Menkes kinky hair syndrome) (rare – UK incidence 1/100,000)
• Copper deficiency
• Aceruloplasminemia^[14]
• Zinc toxicity

Excess

Greater-than-normal ceruloplasmin levels may indicate or be noticed in:

• copper toxicity / zinc deficiency
• pregnancy
• oral contraceptive pill use^[15]
• lymphoma
• acute and chronic inflammation (it is an acute-phase reactant)
• rheumatoid arthritis
• Angina^[16]
• Alzheimer's disease^[17]
• Schizophrenia^[18]
• Obsessive-compulsive disorder^[19]

Reference ranges

Normal blood concentration of ceruloplasmin in humans is 20–50 mg/dL.

Further reading

• Hellman NE, Gitlin JD . Ceruloplasmin metabolism and function . Annual Review of Nutrition . 22 . 439–58 . 2002 . 12055353 . 10.1146/annurev.nutr.22.012502.114457 .
• Mazumder B, Seshadri V, Fox PL . Translational control by the 3'-UTR: the ends specify the means . Trends in Biochemical Sciences . 28 . 2 . 91–8 . Feb 2003 . 12575997 . 10.1016/S0968-0004(03)00002-1 .
• Giurgea N, Constantinescu MI, Stanciu R, Suciu S, Muresan A . Ceruloplasmin - acute-phase reactant or endogenous antioxidant? The case of cardiovascular disease . Medical Science Monitor . 11 . 2 . RA48-51 . Feb 2005 . 15668644 .
• Kingston IB, Kingston BL, Putnam FW . Chemical evidence that proteolytic cleavage causes the heterogeneity present in human ceruloplasmin preparations . Proceedings of the National Academy of Sciences of the United States of America . 74 . 12 . 5377–81 . Dec 1977 . 146197 . 431726 . 10.1073/pnas.74.12.5377 . 1977PNAS...74.5377K . free .
• Polosatov MV, Klimov PK, Masevich CG, Samartsev MA, Wünsch E . Interaction of synthetic human big gastrin with blood proteins of man and animals . Acta Hepato-Gastroenterologica . 26 . 2 . 154–9 . Apr 1979 . 463490 .
• Schilsky ML, Stockert RJ, Pollard JW . Caeruloplasmin biosynthesis by the human uterus . The Biochemical Journal . 288 . 2 . 657–61 . Dec 1992 . 1463466 . 1132061 . 10.1042/bj2880657.
• Walker FJ, Fay PJ . Characterization of an interaction between protein C and ceruloplasmin . The Journal of Biological Chemistry . 265 . 4 . 1834–6 . Feb 1990 . 10.1016/S0021-9258(19)39903-X . 2105310 . free .
• Fleming RE, Gitlin JD . Primary structure of rat ceruloplasmin and analysis of tissue-specific gene expression during development . The Journal of Biological Chemistry . 265 . 13 . 7701–7 . May 1990 . 10.1016/S0021-9258(19)39171-9 . 2332446 . free .
• Yang FM, Friedrichs WE, Cupples RL, Bonifacio MJ, Sanford JA, Horton WA, Bowman BH . Human ceruloplasmin. Tissue-specific expression of transcripts produced by alternative splicing . The Journal of Biological Chemistry . 265 . 18 . 10780–5 . Jun 1990 . 10.1016/S0021-9258(18)87015-6 . 2355023 . free .
• Yang F, Naylor SL, Lum JB, Cutshaw S, McCombs JL, Naberhaus KH, McGill JR, Adrian GS, Moore CM, Barnett DR . Characterization, mapping, and expression of the human ceruloplasmin gene . Proceedings of the National Academy of Sciences of the United States of America . 83 . 10 . 3257–61 . May 1986 . 3486416 . 323492 . 10.1073/pnas.83.10.3257 . 1986PNAS...83.3257Y . free .
• Mercer JF, Grimes A . Isolation of a human ceruloplasmin cDNA clone that includes the N-terminal leader sequence . FEBS Letters . 203 . 2 . 185–90 . Jul 1986 . 3755405 . 10.1016/0014-5793(86)80739-6 . 23472934 .
• Rask L, Valtersson C, Anundi H, Kvist S, Eriksson U, Dallner G, Peterson PA . Subcellular localization in normal and vitamin A-deficient rat liver of vitamin A serum transport proteins, albumin, ceruloplasmin and class I major histocompatibility antigens . Experimental Cell Research . 143 . 1 . 91–102 . Jan 1983 . 6337857 . 10.1016/0014-4827(83)90112-X .
• Kressner MS, Stockert RJ, Morell AG, Sternlieb I . Origins of biliary copper . Hepatology . 4 . 5 . 867–70 . 1984 . 6479854 . 10.1002/hep.1840040512 . 43824397 .
• Takahashi N, Bauman RA, Ortel TL, Dwulet FE, Wang CC, Putnam FW . Internal triplication in the structure of human ceruloplasmin . Proceedings of the National Academy of Sciences of the United States of America . 80 . 1 . 115–9 . Jan 1983 . 6571985 . 393320 . 10.1073/pnas.80.1.115 . 1983PNAS...80..115T . free .
• Dwulet FE, Putnam FW . Complete amino acid sequence of a 50,000-dalton fragment of human ceruloplasmin . Proceedings of the National Academy of Sciences of the United States of America . 78 . 2 . 790–4 . Feb 1981 . 6940148 . 319888 . 10.1073/pnas.78.2.790 . 1981PNAS...78..790D . free .
• Kingston IB, Kingston BL, Putnam FW . Primary structure of a histidine-rich proteolytic fragment of human ceruloplasmin. I. Amino acid sequence of the cyanogen bromide peptides . The Journal of Biological Chemistry . 255 . 7 . 2878–85 . Apr 1980 . 10.1016/S0021-9258(19)85822-2 . 6987229 . free .

External links

• GeneReviews/NCBI/NIH/UW entry on Aceruloplasminemia
• OMIM entries on Aceruloplasminemia

Notes and References

1. Takahashi N, Ortel TL, Putnam FW . Single-chain structure of human ceruloplasmin: the complete amino acid sequence of the whole molecule . Proceedings of the National Academy of Sciences of the United States of America . 81 . 2 . 390–4 . Jan 1984 . 6582496 . 344682 . 10.1073/pnas.81.2.390 . 1984PNAS...81..390T . free .
2. Koschinsky ML, Funk WD, van Oost BA, MacGillivray RT . Marlys Koschinsky . Complete cDNA sequence of human preceruloplasmin . Proceedings of the National Academy of Sciences of the United States of America . 83 . 14 . 5086–90 . Jul 1986 . 2873574 . 323895 . 10.1073/pnas.83.14.5086 . 1986PNAS...83.5086K . free .
3. Royle NJ, Irwin DM, Koschinsky ML, MacGillivray RT, Hamerton JL . Human genes encoding prothrombin and ceruloplasmin map to 11p11-q12 and 3q21-24, respectively . Somatic Cell and Molecular Genetics . 13 . 3 . 285–92 . May 1987 . 3474786 . 10.1007/BF01535211 . 45686258 .
4. Holmberg CG, Laurell CB . Investigations in serum copper. II. Isolation of the Copper containing protein, and a description of its properties . Acta Chem Scand . 1948 . 2 . 550–56 . 10.3891/acta.chem.scand.02-0550. free .
5. Book: O'Brien PJ, Bruce WR . Endogenous Toxins: Targets for Disease Treatment and Prevention, 2 Volume Set . 2009 . John Wiley & Sons. 978-3-527-32363-0 . 405–6 .
6. Hellman NE, Gitlin JD . Ceruloplasmin metabolism and function . Annual Review of Nutrition . 22 . 439–58 . 2002 . 12055353 . 10.1146/annurev.nutr.22.012502.114457 .
7. Song D, Dunaief JL . Retinal iron homeostasis in health and disease . Frontiers in Aging Neuroscience . 5 . 24 . 2013 . 23825457 . 10.3389/fnagi.2013.00024 . 3695389. free .
8. Book: Bertini, Ivano. Biological Inorganic Chemistry. University Science Books. 2007. 978-1-891389-43-6. California, USA. 426–442. English.
9. Book: Bertini, Ivano. Biological Inorganic Chemistry. University Science Books. 2007. 978-1-891389-43-6. California, USA. 426–442. English.
10. Sampath P, Mazumder B, Seshadri V, Fox PL . Transcript-selective translational silencing by gamma interferon is directed by a novel structural element in the ceruloplasmin mRNA 3' untranslated region . Molecular and Cellular Biology . 23 . 5 . 1509–19 . Mar 2003 . 12588972 . 151701 . 10.1128/MCB.23.5.1509-1519.2003 .
11. Mazumder B, Sampath P, Fox PL . Regulation of macrophage ceruloplasmin gene expression: one paradigm of 3'-UTR-mediated translational control . Molecules and Cells . 20 . 2 . 167–72 . Oct 2005 . 10.1016/S1016-8478(23)13213-4 . 16267389 . free .
12. Web site: Ceruloplasmin Test: MedlinePlus Medical Test. 2021-12-10. medlineplus.gov. en.
13. Scheinberg IH, Gitlin D . Deficiency of ceruloplasmin in patients with hepatolenticular degeneration (Wilson's disease) . Science . 116 . 3018 . 484–5 . Oct 1952 . 12994898 . 10.1126/science.116.3018.484 . 1952Sci...116..484S .
14. Gitlin JD . Aceruloplasminemia . Pediatric Research . 44 . 3 . 271–6 . Sep 1998 . 9727700 . 10.1203/00006450-199809000-00001 . free .
15. Elkassabany NM, Meny GM, Doria RR, Marcucci C . Green plasma-revisited . Anesthesiology . 108 . 4 . 764–5 . Apr 2008 . 18362615 . 10.1097/ALN.0b013e3181672668 . free .
16. Ziakas A, Gavrilidis S, Souliou E, Giannoglou G, Stiliadis I, Karvounis H, Efthimiadis G, Mochlas S, Vayona MA, Hatzitolios A, Savopoulos C, Pidonia I, Parharidis G . Ceruloplasmin is a better predictor of the long-term prognosis compared with fibrinogen, CRP, and IL-6 in patients with severe unstable angina . Angiology . 60 . 1 . 50–9 . 2009 . 18388036 . 10.1177/0003319708314249 . 843454 .
17. Lutsenko S, Gupta A, Burkhead JL, Zuzel V . Cellular multitasking: the dual role of human Cu-ATPases in cofactor delivery and intracellular copper balance . Archives of Biochemistry and Biophysics . 476 . 1 . 22–32 . Aug 2008 . 18534184 . 2556376 . 10.1016/j.abb.2008.05.005 .
18. Wolf TL, Kotun J, Meador-Woodruff JH . Plasma copper, iron, ceruloplasmin and ferroxidase activity in schizophrenia . Schizophrenia Research . 86 . 1–3 . 167–71 . Sep 2006 . 16842975 . 10.1016/j.schres.2006.05.027 . 38267889 .
19. Virit O, Selek S, Bulut M, Savas HA, Celik H, Erel O, Herken H . High ceruloplasmin levels are associated with obsessive compulsive disorder: a case control study . Behavioral and Brain Functions . 4 . 52 . 2008 . 19017404 . 2596773 . 10.1186/1744-9081-4-52 . free .