Molecular pathology of ceruloplasmin

Preliminary X-ray crystallographic and physico-chemical investigations of human ceruloplasmin

Single crystals of the plasma protein ceruloplasmin (CP) and its two modified forms: neuraminidase-treated CP (asialoCP) and NaN3-inhibited CP (NaN3-CP) suitable for X-ray studies have been grown. The native CP crystallizes as described previously by Magdoff-Fairchield et al. (1969) in the tetragonal space group 14 (a = b = 268.2 A, c = 129.1 A) with two protein molecules in the asymmetric part of a unit cell. AsialoCP crystals belong to the trigonal space group P 3(1)21 or P321 (a = b = 215.0 A, c = 84.5 A) and have one protein molecule in the asymmetric part of a unit cell. NaN3-CP crystals are isomorphous to crystals of native CP. Despite some differences in electrophoretic mobility and optical properties, the conformations of the native CP molecule and its modified forms are similar, as can be concluded from a study of ORD and CD spectra.

Analysis of seven pedigrees of childhood Wilson's disease characterized by abdominal symptoms

In a survey of childhood Wilson's disease (WD) characterized by abdominal symptoms, three patients with high levels of immunologically detectable ceruloplasmin (CP) in serum were found. These three cases were compared with typical cases of WD in which serum CP level was low. In order to clarify the cause of WD, serum CP levels were quantified by two methods, an immunological protein assay and an oxidase activity assay. Using the results of these two assays, WD cases were classified into three groups on the basis of CP content; the first group consisted of patients with low enzyme activity and low CP protein content, the second group consisted of patients with low enzyme activity and normal CP protein content, and the third group, those patients with normal enzyme activity and normal CP protein content. No significant difference in symptoms was observed between these three groups. Since relatively high levels of CP were detected in some WD patients, genetic variation in CP in WD patients was examined by restriction enzyme fragment length polymorphism analysis using CP cDNA. However, no large deletion in the CP gene was detected. Using four types of gene probes for chromosome 13 known to be related to WD, the DNA of WD patients was examined in a similar fashion, but no significant difference was observed between the groups.

Copper deficiency secondary to a copper transport defect: a new copper metabolic disturbance

We describe a 21-year-old man who developed copper deficiency manifested as a demyelinating neuropathy, chronic intestinal pseudo-obstruction, osteoporosis, testicular failure, retinal degeneration, and cardiomyopathy with a tortuous aorta. His serum copper was low and did not increase despite administration of large doses of intravenous copper sulfate. The ceruloplasmin level as measured by an antibody technique was normal, yet ceruloplasmin (Cp) oxidase activity was very low. The Cp amino acid sequence was normal. This suggests that the copper deficiency was caused by a defect in hepatic processing of copper for incorporation into Cp.

Molecular studies of ceruloplasmin deficiency in Wilson's disease

Deficiency of serum ceruloplasmin is a characteristic biochemical abnormality of Wilson's disease, although the mechanism of this finding is unknown. Ceruloplasmin messenger RNA (mRNA) levels were therefore examined in five patients with Wilson's disease and five controls with other types of hepatic disease. Northern and dot blot hybridizations showed that detectable ceruloplasmin mRNA was present in all of the patients with Wilson's disease, including one patient with no detectable serum ceruloplasmin. However, the ceruloplasmin mRNA levels in the Wilson's disease patients were only 33% that of controls (P less than 0.001). In contrast, albumin mRNA levels in the Wilson's disease patients averaged 161% that of controls. In an attempt to better delineate the level of gene expression responsible for this decrease in ceruloplasmin mRNA, the nuclear run-on assay was used to analyze transcriptional rates. The amount of ceruloplasmin gene transcription in four Wilson's patients was decreased to 44% that of three controls. These results indicate that the diminished serum ceruloplasmin levels in patients with Wilson's disease are due at least in part to a decrease in ceruloplasmin gene transcription.

Electrophoresis and immunoblot of cerebrospinal fluid proteins in spasmodic torticollis

Protein patterns of cerebrospinal fluid (CSF) from patients with spasmodic torticollis (ST) were investigated to determine whether abnormalities previously reported could be detected and further identified. CSF was collected from 12 patients with ST and 6 normal controls. The CSF proteins were analyzed using sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis and silver staining. In 11 of the 12 patients with ST, a CSF protein pattern was observed which differed from that in the controls. The identity of the abnormal proteins was ascertained by blotting and immunostaining with specific antisera to IgG and ceruloplasmin (Cp). CSF from 2 of 12 patients had distinct bands staining for IgG and 7 had abnormal immunostaining for Cp.

Evidence that human ceruloplasmin molecule consists of homologous parts

The products of spontaneous and induced proteolysis of human ceruloplasmin (Cp) were studied. Some physico-chemical properties of the six fragments with electrophoretically determined Mr 130,000 (F1), 110,000 (F2), 66,000 (F3), 48,000 (F4) 22,000 (F5) and 18,000 (F6) were compared. The amino acid compositions and N-terminal amino acid sequences coincide in F1-F5, but differ from those of F6. Limited tryptic proteolysis of Cp causes the accumulation of polypeptide fragment with Mr 22,000, the N-terminal primary structure of which is identical to that of F5 produced by spontaneous proteolysis. Electrophoretic fragments of Cp were extracted from polyacrylamide gel, treated with 125I and then studied by peptide mapping with subsequent radioautography. The comparison of the "finger prints" showed the identity of F1 to F2 and F3 and gross similarity between F4 and F1-F3. It also revealed similar peptides in F5 and F6 hydrolyzates and almost perfect matching of the F4 map to the map of F5 + F6 mixture. On the basis of the obtained data general principles of Cp molecular organization are discussed and intramolecular homology is suggested to be a feature of the protein.

Preproceruloplasmin is a primary product of cell-free translation of ceruloplasmin messenger RNA

Biosynthesis of ceruloplasmin was studied in wheat germ extract programmed with polysomal RNA from rat liver. Optimal potassium concentration for the total protein-synthesizing activity and for the synthesis of immunoreactive ceruloplasmin was 96 and 186 mM respectively. 7-methylguanosine 5'-monophosphate caused two-fold inhibition of the cell-free synthesis of ceruloplasmin. Immunoprecipitated ceruloplasmin that was synthesized at optimal potassium concentration was a homogeneous polypeptide of a molecular weight about 84 kD. The addition of membrane fractions from rat liver to the incubation mixture caused the conversion of the 84 kD polypeptide into 80 kD and 65 kD polypeptides that are similar to proceruloplasmins synthesized in rat liver during in vivo pulse labelling. The suggestion is made that 84 kD polypeptide is a primary product of the translation of ceruloplasmin mRNA (preproceruloplasmin).

Highly purified ceruloplasmin messenger RNA from rat liver. Physico-chemical and functional characteristics

Highly purified ceruloplasmin mRNA was isolated from rat liver polyribosomes. The molecular weight of ceruloplasmin mRNA is in a range from 1.05 to 1.25 . 10(6) daltons which is large enough to code for a putative precursor of ceruloplasmin (approximately 700 amino acid acids). Ceruloplasmin mRNA contains 3'-terminal poly(A) the length of which varies from 38 to 165 nucleotides. The 5'-end of ceruloplasmin mRNA is blocked with confronting m7G residue which is a component of cap I (m7G5'ppp5'XmpAp). The addition of ceruloplasmin mRNA to wheat-germ cell free system programmed the synthesis of a product that was largely precipitated by anti-ceruloplasmin immunoglobulins. The translation product was homogeneous in polyacrylamide gel-sodium dodecylsulfate electrophoresis. Cell-free translation of ceruloplasmin mRNA was sensitive to inhibition by cap analogue.

Complex molecular structure of the gene coding for rat ceruloplasmin

The distribution of ceruloplasmin-coding sequences among the fragments of rat nuclear DNA obtained after the complete digestion with seven restriction endonucleases (EcoRI, BamHI, BspI, HindIII, KpnI, BglII and XhoI) was studied using highly specific cDNA probes. Although only a single copy of this gene per rat haploid genome was detected in DNA-cDNA hybridization in solution, the number of restriction fragments carrying the sequences of ceruloplasmin (CP) gene varied from two to five, depending upon the enzyme used, and their total length was several times higher than the minimal length of CP-coding gene, as deduced from the size of mRNA (2.3 Md for double-stranded DNA). The partial double stranded DNA transcript of ceruloplasmin mRNA coding for about 70% of its length (from 3'-end) does not contain recognition sites for some restriction endonucleases generating multiple fragments of CP gene in cellular DNA. These data are consistent with a split pattern of CP gene which seems to consist of several exons and introns. The partial protection from S1 nuclease of discrete fragments of full-length cDNA after annealing with high molecular weight nuclear RNA is consistent with this assumption and seems to be an indication that exons and introns are joined into a functional unit coding for high mol wt. CP pre-mRNA.

Electron microscope study on human ceruloplasmin

Electron microscopy of human ceruloplasmin (CP) molecules revealed a few distinctive types of particle images. Analysis of these images allows to propose a tentative model for CP: six "subunits" (which we call domains) not much different in size are arranged with 32 point group pseudosymmetry. The determination of the number of polypeptides arising at the spontaneous specific proteolytic fragmentation of CP and their molecular weights conform with this assumption. The electrophoretic studies of the CP samples prepared both with and without potent proteolytic inhibitor, PMSF, revealed that CP is a single-chain protein with molecular weight of 130 000. Isolated and stored without PMSF the polypeptide chain of CP undergoes specific proteolytic cleavage which results in the appearance of polypeptides with molecular weights of 16 000, 48 000, and 64 000. The latter two polypeptides degradate to about two- and three-fold decreased molecular weights fragments, respectively. Therefore, the single polypeptide chain of CP contains at least five peptide bonds which are particularly susceptible to proteolytic attack and which connect six principal segments of the chain. The hydrolysis of these bonds results in liberation of the six fragments which were integrated in the enzymatically active globule of CP.

Isolation and partial purification of ceruloplasmin messenger RNA from rat liver

Partially purified ceruloplasmin mRNA was isolated using indirect immunoprecipitation of rat liver polysomes and poly(U)-Sepharose chromatography of polysomal RNA. This RNA programmed the synthesis of ceruloplasmin polypeptides in a cell-free system from mitochondria. Immunochemical analysis of the translation products revealed a 40-fold enrichment of the ceruloplasmin mRNA activity. The purified ceruloplasmin mRNA migrated as a major homogeneous component with an apparent molecular weight about 1 X 10(6) daltons in polyacrylamide gels containing sodium dodecyl sulfate. The immunoprecipitated products of the cell-free translation had molecular weights in the range 4.5--5.4 X 10(4) daltons as estimated by gel-electrophoresis under denaturating conditions. These values approach the weight of the half-molecule of native ceruloplasmin.

On the defect of synthesis ceruloplasmin in the liver polyribosomes in Wilson's disease

Comparative immunochemical analysis of ceruloplasmin-synthesizing polyribosomes in liver biopsies from control subjects and homozygous carriers of the Wilson's mutation was performed. According to I125-antibody binding data, the amount of ceruloplasmin-forming liver polysomes in patients with Wilson's disease was 10--20 times lower than that in non-Wilson patients. Correspondingly, the pulse labeling of ceruloplasmin polypeptides was decreased several-fold in the cell-free liver preparations from patients with Wilson's disease.