Spectroscopic and photoreduction studies of copper chromophores in ceruloplasmin

Cu(I/II) redox control of molecular conformation and shape in chiral tripodal ligands: binary exciton-coupled circular dichroic states

This manuscript describes the design, synthesis, and characterization of a coordination complex that demonstrates reversible interconversion between two redox states that show very different chiroptical properties. Reported here are three chiral N(4)-tetradentate ligands, prepared in enantiopure form by asymmetric synthesis, and their circular dichroic and other properties, as well as those of numerous Cu(I) and Cu(II) complexes. While the chiroptical spectra of the free ligands are unremarkable, the CD spectra of the complexes are very intense, and spectral features indicate that they derive from exciton coupling. Comparison of complexes with one, two, or three chromophores provides strong supportive evidence for this assignment, and semiquantitative correlation with intensity as rationalized by additivity. A Cu(I)(L)/Cu(II)(L) redox couple was identified that showed dramatically different circular dichroic properties that was further shown to be easily oxidized and reduced chemically between two states with remarkable retention of signal. A structural hypothesis for the interconversion is given and supported by a variety of spectroscopic evidence.

The possible role of copper ions in atherogenesis: the Blue Janus

It has been proposed that the oxidative modification of low density lipoprotein (LDL) is a key event in human atherogenesis. Copper ions can catalyse the oxidative modification of LDL in vitro and there is some evidence that they may also participate in the oxidation of LDL within the arterial wall. However, copper ions also form an intrinsic constituent of superoxide dismutase and caeruloplasmin, enzymes that may be involved in preventing oxidative injury. Atherosclerotic lesions frequently contain considerable quantities of extracellular matrix molecules. These may contribute to the expansion of the arterial neointima, causing luminal narrowing. They may also play a beneficial role by stabilising the plaque. Copper is an essential component of lysyl oxidase, an enzyme involved in the biosynthesis of collagen, which is a major constituent of the extracellular matrix. The impact of alterations in body copper status on atherogenesis is therefore difficult to predict. Experimental and epidemiological data are conflicting and therefore do not provide a clear resolution of this issue. We have reviewed the biochemical and cellular effects of copper ions that may play a role in atherogenesis.

Effects of oxidative stress on some physiochemical properties of caeruloplasmin

We report the effects of oxidative stress generated by low-intensity u.v. irradiation (366 and 254 nm), dialysis against ascorbate and isolated stimulated neutrophils on some physicochemical properties of caeruloplasmin. Low-intensity u.v. irradiation resulted in a loss of ferroxidase activity and 610 nm absorption, changes previously reported to occur during storage and manipulation of caeruloplasmin. These alterations were found to correspond to aggregation of the protein, induction of visible fluorescence (excitation, 360 nm; emission, 454 nm), changes in c.d. spectra which were indicative of alterations in protein conformation, loss of half-cystine, tryptophan and tyrosine content and loss immunoreactivity. The changes in the far-u.v. c.d. spectrum of caeruloplasmin were more pronounced than those observed for u.v.-irradiated IgG. Similar c.d. changes and induction of fluorescence were observed following dialysis of caeruloplasmin against ascorbate or exposure to stimulated neutrophils. It is concluded that the lability of caeruloplasmin may arise from oxidative modification, in addition to the previously described susceptibility of this protein to proteolysis.

Isolation and partial nucleotide sequence of the laccase gene from Neurospora crassa: amino acid sequence homology of the protein to human ceruloplasmin

The laccase (benzenediol:oxygen oxidoreductase, EC 1.10.3.2) gene from Neurospora crassa was cloned and part of its nucleotide sequence corresponding to the carboxyl-terminal region of the protein has been determined. The gene was cloned by cDNA synthesis with a laccase-specific synthetic deoxyundecanucleotide as primer and poly(A) RNA isolated from cycloheximide-treated N. crassa cultures as template. Based on the nucleotide sequence of the cDNA obtained, a unique 21-mer was synthesized and used to screen a genomic DNA library from N. crassa. Five different positive clones were isolated and shown to share an overlapping DNA region with the same pattern of restriction sites. Sequence analysis of the common 1.36-kilobase Sal I fragment revealed an open reading frame of 726 nucleotides. The amino acid sequence deduced is in complete agreement with the primary structures of several tryptic peptides isolated previously from N. crassa laccase. The analyzed carboxyl-terminal region of laccase exhibits a striking sequence homology to the carboxyl-terminal part of the third homology unit of the multicopper oxidase ceruloplasmin and to a smaller extent, to the low molecular weight blue copper proteins plastocyanin and azurin. Based on amino acid sequence comparison between these proteins, putative copper ligands of N. crassa laccase are proposed. Moreover, these data further support the hypothesis that the small blue copper proteins and the multicopper oxidases have evolved from the same ancestral gene.

The effect of some anions on the spectral properties of bovine ceruloplasmin

The effect of binding of N3-, SCN-, OCN-, and F- to bovine ceruloplasmin (Cp) has been studied in detail using absorption, circular dichroic (CD), and electron paramagnetic resonance (EPR) spectroscopies. With the addition of increasing amounts of N3-, SCN-, and OCN- to a Cp solution, the intensity of the band at 614 nm at first increased several percent and then decreased gradually as at least one type I copper was reduced and/or as the type I copper was changed to type II copper. Concomitantly, new bands appeared at 430 and 365 nm for N3-, 435 and 380 nm for SCN-, and about 390 nm for OCN-. A conformational change in the protein induced by the binding of N3-, SCN-, and OCN- to the type II and type III coppers led to the change in the CD spectra. The observed increase of the band at about 430 nm was attributed to the change occurring at the type I copper site. On the other hand, the band at about 370 nm may come from a charge transfer of coordinated anions to the Cu(II) ion. Fluoride ion did not induce the appearance of the band at around 430 and 370 nm, but the parallel component of the type II copper EPR signal was split upon the binding of two fluoride ions to the copper ion.

Reaction of human ceruloplasmin and anion treated ceruloplasmin with diethyldithiocarbamate

The reaction of human ceruloplasmin and anion treated ceruloplasmin with diethyldithiocarbamate was studied at pH 5.5. The analysis of optical and EPR spectra at 9 GHz showed that ceruloplasmin contains five paramagnetic copper ions, two of which, X and Y, not involved in enzymatic activity, are chelated by diethyldithiocarbamate; the complex thus formed is easily removed by high-speed centrifugation. However, the enzyme depleted of these two X and Y copper ions is able to compete with the Cu(II)-diethyldithiocarbamate complex, as time elapses, recovering both Cu(II) atoms. In addition diethyldithiocarbamate acts as a reducing agent for the two type-I copper atoms when added in large excess to the enzyme or the anion treated enzyme.

Structural model of human ceruloplasmin based on internal triplication, hydrophilic/hydrophobic character, and secondary structure of domains

A molecular model for the structure of human ceruloplasmin is proposed that is based on the determination of the complete amino acid sequence, studies of the products of limited proteolytic cleavage, calculations of the hydrophilic/hydrophobic character (hydropathy profile), and predictions of the local secondary structure. This multicopper oxidase (Mr approximately 132,000) consists of a single polypeptide chain (1046 amino acid residues) with four attached glucosamine oligosaccharides. Computer-assisted statistical analysis of the internal repetition in the amino acid sequence confirms that the entire polypeptide chain is divided into three contiguous homology units, each containing about 350 amino acid residues. Each homology unit is subdivided into three domains, designated A1, A2, and B, that differ in structure and probably in function. Calculations of the hydropathy profile and predictions of the secondary structure support a molecular model based on internal repetition of three homology units and help to identify characteristic features of the interdomain junctions. The alignment scores for internal duplication of pairings of the three homology units of ceruloplasmin exceed the scores yet reported for contiguous internal duplication of any other protein. This highly significant evidence for intragenic repetition suggests that the ceruloplasmin molecule evolved by tandem triplication of ancestral genes coding for a primordial copper oxidase.