Ceruloplasmin

Abstract

Ceruloplasmin is a multi‐copper oxidase that contains most of the copper present in the plasma. It is an acute‐phase reactant that exhibits a two‐ to three‐fold increase over the normal concentration of 300 mg ml −1 in adult plasma. However, the precise physiological role(s) of ceruloplasmin has been the subject of intensive debate and it is likely that the enzyme has a multi‐functional role, including iron oxidase activity and oxidation of biogenic amines. The three‐dimensional X‐ray structure of the human enzyme shows that the molecule is composed of six cupredoxin‐type domains arranged in a triangular array. There are six integral copper atoms per molecule (mononuclear sites in domains 2, 4, and 6 and a trinuclear site between domains 1 and 6) and two labile sites with roughly 50% occupancy. Further structural studies on the binding of metal cations by the enzyme have indicated a putative mechanism for ferroxidase activity. Other studies have located the binding sites for an inhibitor (azide) and various substrates [aromatic diamines, biogenic amines, and D ‐lysergic acid diethylamide (LSD)]. The binding site of the azide moiety is topologically equivalent to one of the sites reported for ascorbate oxidase. However, there are two distinct binding sites for amine substrates; aromatic diamines bind at the base of domain 4 remote from the mononuclear copper site, whereas the biogenic amine series typified by serotonin, epinephrine, and dopa bind in close vicinity to that site utilized by cations in domain 6 and close to the mononuclear copper.

Cupredoxin-like domains in haemocyanins

“…In principle, the combination of several copper centres is not unusual. Blue oxidases, such as laccase, ascorbate oxidase and ceruloplasmin, combine a mixed type 2 and type 3 copper centre along with a type 1 copper centre [37][38][39]. However, the combination of a pure type 3 copper centre and a type 1 copper centre in a single protein, as we suggest in the present paper for ancestral haemocyanins, is unprecedented.…”

Discrete Roles of Copper Ions in Chemical Unfolding of Human Ceruloplasmin

“…Because the holo-intermediate has lost about 30−40% of its secondary structure (which equals two out of six domains) and two coppers, one being an oxidized T1 copper (based on the blue color change), it is possible that domains 2 (containing silent T1C) and 4 (containing T1B) are unfolded in I 4Cu . Notably, the disulfide bonds in domains 2 and 4 link different β-strands as compared to the disulfide bonds in domains 1, 3, and 5 ( , ); this may account for differential domain stability. Earlier work () gives support that T1B, and not T1A, is the oxidized T1 copper removed in the unfolding intermediate.…”

“…In humans, CP accounts for ∼95% of the plasma copper and plays an important role in iron metabolism due to its ability to oxidize Fe 2+ to Fe 3+ , which allows for subsequent incorporation of Fe 3+ into apotransferrin ( − ). CP is also believed to function as an antioxidant agent to scavenge free radicals, as an amine oxidase to control levels of biogenic amines, and as a copper transporter to deliver copper to extrahepatic tissues ( − ). CP is synthesized in hepatocytes and secreted into the plasma after incorporation of six copper ions in the secretory pathway ().…”

“…CP consists of a 1046 residue polypeptide and six integral copper ions classified into five different sites ( , ). The crystal structure of CP ( , ) demonstrates that the polypeptide is folded in six β-barrel domains arranged in three pairs forming a triangular array around a pseudo 3-fold axis (Figure ). Three copper ions are found in type 1 (T1) mononuclear centers located in domains 2, 4, and 6.…”

“…Three copper ions are found in type 1 (T1) mononuclear centers located in domains 2, 4, and 6. Copper in domains 4 (T1B) and 6 (T1A) is coordinated by two His, one Cys, and one Met, whereas the Met is absent in the metal-binding site in domain 2 (T1C) ( , ). The high reduction potential of the T1C copper indicates that it is permanently reduced and not catalytically relevant ( , ).…”