An X-ray crystallographic study of the binding sites of the azide inhibitor and organic substrates to ceruloplasmin, a multi-copper oxidase in the plasma.
Ceruloplasmin is a multi-copper oxidase, which 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 microg/ml 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 the oxidation of biogenic amines. The three-dimensional X-ray structure of the human enzyme was elucidated in 1996 and showed that the molecule was 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 indicated a putative mechanism for ferroxidase activity. In this paper we report medium-resolution X-ray studies (3.0-3.5 A) which locate the binding sites for an inhibitor (azide) and various substrates [aromatic diamines, biogenic amines and (+)-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 on the bottom 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 utilised by cations in domain 6 and close to the mononuclear copper. These binding sites are discussed in terms of possible oxidative mechanisms. The binding site for LSD is also reported.
Zaitsev
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CCLRC Daresbury Laboratory, Warrington, Cheshire WA4 4AD, UK.
Zaitseva
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Papiz
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Lindley
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D001386:Azides / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D001665:Binding Sites; D002570:Ceruloplasmin / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism; D018360:Crystallography, X-Ray; D004295:Dihydroxyphenylalanine / Q000737:chemistry; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D004837:Epinephrine / Q000737:chemistry; D006801:Humans; D008238:Lysergic Acid Diethylamide / Q000737:chemistry; D008958:Models, Molecular; D009638:Norepinephrine / Q000737:chemistry; D010088:Oxidoreductases / Q000097:blood* / Q000737:chemistry; D010655:Phenylenediamines / Q000737:chemistry; D011487:Protein Conformation; D012701:Serotonin / Q000737:chemistry; D013379:Substrate Specificity
D001386:Azides; D004791:Enzyme Inhibitors; D010655:Phenylenediamines; D012701:Serotonin; D004295:Dihydroxyphenylalanine; D008238:Lysergic Acid Diethylamide; D010088:Oxidoreductases; C024748:copper oxidase; D002570:Ceruloplasmin; C029728:4-phenylenediamine; D009638:Norepinephrine; D004837:Epinephrine