Molecular Aspects of a Robust Assay for Ferroxidase Function of Ceruloplasmin

Activation of vitamin D receptor inhibits Tau phosphorylation is associated with reduction of iron accumulation in APP/PS1 transgenic mice

Vitamin D deficiency and iron accumulation are prevalent in the brains of Alzheimer's disease (AD) patients, however, whether Vitamin D has a role in the regulations of iron metabolism in the condition of AD remains unknown. Our previous studies revealed that vitamin D deficiency promotes β-amyloid (Aβ) deposition in the APP/PS1 mouse brains, while supplemented with a specific agonist of vitamin D receptor (VDR), paricalcitol (PAL), significantly reduced Aβ production via promoting the lysosomal degradation of β-site APP cleavage enzyme 1 (BACE1). In this study, our data suggested that activation of VDR by PAL significantly reduced the iron accumulation in the cortex and hippocampus of APP/PS1 mice through downregulation of Transferrin receptor (TFR) by reducing iron-regulatory protein 2 (IRP2) expression. Furthermore, activation of VDR effectively reduced the phosphorylations of Tau at Ser396 and Thr181 sites via inhibiting the GSK3β phosphorylation (Tyr216). Taken together, our data suggest that activation of VDR could inhibit the phosphorylations of Tau possibly by repressing the iron accumulation-induced upregulation of GSK3β activity in the brains of APP/PS1 mice. Thus, activation of VDR may be an effective strategy for treating AD.

Therapeutic potential of iron modulating drugs in a mouse model of multiple system atrophy

Multiple System Atrophy (MSA) is a rare neurodegenerative synucleinopathy which leads to severe disability followed by death within 6-9 years of symptom onset. There is compelling evidence suggesting that biological trace metals like iron and copper play an important role in synucleinopathies like Parkinson's disease and removing excess brain iron using chelators could slow down the disease progression. In human MSA, there is evidence of increased iron in affected brain regions, but role of iron and therapeutic efficacy of iron-lowering drugs in pre-clinical models of MSA have not been studied. We studied age-related changes in iron metabolism in different brain regions of the PLP-αsyn mice and tested whether iron-lowering drugs could alleviate disease phenotype in aged PLP-αsyn mice. Iron content, iron-ferritin association, ferritin protein levels and copper-ceruloplasmin association were measured in prefrontal cortex, putamen, substantia nigra and cerebellum of 3, 8, and 20-month-old PLP-αsyn and age-matched non-transgenic mice. Moreover, 12-month-old PLP-αsyn mice were administered deferiprone or ceruloplasmin or vehicle for 2 months. At the end of treatment period, motor testing and stereological analyses were performed. We found iron accumulation and perturbed iron-ferritin interaction in substantia nigra, putamen and cerebellum of aged PLP-αsyn mice. Furthermore, we found significant reduction in ceruloplasmin-bound copper in substantia nigra and cerebellum of the PLP-αsyn mice. Both deferiprone and ceruloplasmin prevented decline in motor performance in aged PLP-αsyn mice and were associated with higher neuronal survival and reduced density of α-synuclein aggregates in substantia nigra. This is the first study to report brain iron accumulation in a mouse model of MSA. Our results indicate that elevated iron in MSA mice may result from ceruloplasmin dysfunction and provide evidence that targeting iron in MSA could be a viable therapeutic option.

Principles and practice of determining metal-protein affinities

Metal ions play many critical roles in biology, as structural and catalytic cofactors, and as cell regulatory and signalling elements. The metal–protein affinity, expressed conveniently by the metal dissociation constant, K_D, describes the thermodynamic strength of a metal–protein interaction and is a key parameter that can be used, for example, to understand how proteins may acquire metals in a cell and to identify dynamic elements (e.g. cofactor binding, changing metal availabilities) which regulate protein metalation in vivo. Here, we outline the fundamental principles and practical considerations that are key to the reliable quantification of metal–protein affinities. We review a selection of spectroscopic probes which can be used to determine protein affinities for essential biological transition metals (including Mn(II), Fe(II), Co(II), Ni(II), Cu(I), Cu(II) and Zn(II)) and, using selected examples, demonstrate how rational probe selection combined with prudent experimental design can be applied to determine accurate K_D values.

Calculating metalation in cells reveals CobW acquires CoII for vitamin B12 biosynthesis while related proteins prefer ZnII

Protein metal-occupancy (metalation) in vivo has been elusive. To address this challenge, the available free energies of metals have recently been determined from the responses of metal sensors. Here, we use these free energy values to develop a metalation-calculator which accounts for inter-metal competition and changing metal-availabilities inside cells. We use the calculator to understand the function and mechanism of GTPase CobW, a predicted Co^II-chaperone for vitamin B₁₂. Upon binding nucleotide (GTP) and Mg^II, CobW assembles a high-affinity site that can obtain Co^II or Zn^II from the intracellular milieu. In idealised cells with sensors at the mid-points of their responses, competition within the cytosol enables Co^II to outcompete Zn^II for binding CobW. Thus, Co^II is the cognate metal. However, after growth in different [Co^II], Co^II-occupancy ranges from 10 to 97% which matches CobW-dependent B₁₂ synthesis. The calculator also reveals that related GTPases with comparable Zn^II affinities to CobW, preferentially acquire Zn^II due to their relatively weaker Co^II affinities. The calculator is made available here for use with other proteins.

Role of a Tyrosine Radical in Human Ceruloplasmin Catalysis

Multicopper oxidases (MCOs) are a large family of diverse enzymes found in both eukaryotes and prokaryotes that couple one-electron oxidations of various substrates to the four-electron reduction of O2 to H2O, functioning through a set of metallocofactors consisting of one type 1 copper (T1 Cu) and one trinuclear copper cluster (TNC). Human serum ceruloplasmin (Cp) is a unique member of MCOs composed of six cupredoxin domains and harbors six Cu ions arranged as three T1 Cu and one TNC. The native substrate of Cp is Fe2+. It is an essential ferroxidase critical for iron homeostasis and is closely associated with metal-mediated diseases and metal neurotoxicity. In human serum, Cp operates under substrate-limiting low [Fe2+] but high [O2] conditions, implying the possible involvement of partially reduced intermediates in Cp catalysis. In this work, we studied for the first time Cp reactivities at defined partially reduced states and discovered a tyrosine radical weakly magnetically coupled to the native intermediate (NI) of the TNC via a hydrogen bond. Our results lead to a new hypothesis that human iron transport is regulated as the paired transfer of iron from ferroportin to Cp to transferrin, and the tyrosine residue in Cp acts as a gate to avoid reactive oxygen species (ROS) formation when Fe2+ delivery is dysregulated.

Insights from molecular dynamics simulation of human ceruloplasmin (ferroxidase enzyme) binding with biogenic monoamines

Human ceruloplasmin (hCP) is a multi-copper oxidase with ferroxidase and amine oxidase activities. Molecular dynamics simulation (MDS) and docking analysis of biogenic monoamines with ceruloplasmin explain the role of Asp1025, Glu935, Glu272, Glu232 and Glu230 together with the binding site water molecules (referred as conserved water molecules) in the stabilization of neurotransmitter (Serotonin, Norepinephrine and Epinephrine) molecules within the binding cavity of hCP. Conserved water molecules are found at specific positions interacting with the protein structures that have sequence similarity. The ethylamine side chain nitrogen atom (N1) of neurotransmitter molecules interacts with water molecules in the binding cavity formed by Asp1025, Glu935 and Glu232 residues. These residues form an acidic triad mimicking a substrate binding cavity. The hydroxyl groups attached to the catechol ring of epinephrine and norepinephrine have been stabilized by Asp230 and Asp232 residues. Data suggests that the recognition of biogenic amines mediates through the N+(amine) ...Asp1025-His1026-CuCis-His path. The potential recognition path of biogenic monoamines to trinuclear copper cluster supported by active site water molecules (referred as conserved water molecules) is described in this report.

Value of immune factors for monitoring risk of lung cancer in patients with interstitial lung disease

Objective

Patients with interstitial lung disease (ILD) are at increased risk of developing lung cancer. We aimed to investigate the clinical significance of serum immune factors in this progression.

Methods

We retrospectively screened a hospital database from January 2012 to December 2016 for patients with lung cancer and ILD. We measured serum levels of C3, C4, IgA, IgG, IgM, C-reactive protein (CRP), ceruloplasmin (CER), and rheumatoid factor in these patients and in healthy controls.

Results

We analyzed data for 262 patients with lung cancer, 220 with ILD, and 57 healthy controls. CER levels were significantly higher in patients with lung cancer (0.35 ± 0.10 g/L) compared with both ILD patients (0.31 ± 0.25 g/L) and healthy individuals (0.25 ± 0.04 g/L). C3 and C4 levels were both significantly higher in healthy individuals compared with patients with lung cancer (C3: 1.70 ± 0.29 vs 1.04 ± 0.26 g/L, C4: 0.27 ± 0.24 vs 0.24 ± 0.09 g/L) and ILD (C3: 1.70 ± 0.29 vs 0.97 ± 0.25 g/L, C4: 0.27 ± 0.24 vs 0.21 ± 0.09 g/L). Optimal scaling analysis demonstrated that lung cancer was closely associated with CRP, CER, C3, and C4.

Conclusions

Increased levels of CRP and CER and decreased levels of C3 and C4 may identify patients with ILD at high risk of developing lung cancer.

Chloride Control of the Mechanism of Human Serum Ceruloplasmin (Cp) Catalysis

Unraveling the mechanism of ceruloplasmin (Cp) is fundamentally important toward understanding the pathogenesis of metal-mediated diseases and metal neurotoxicity. Here we report that Cl^-, the most abundant anion in blood plasma, is a key component of Cp catalysis. Based on detailed spectroscopic analyses, Cl^- preferentially interacts with the partially reduced trinuclear Cu cluster (TNC) in Cp under physiological conditions and shifts the electron equilibrium distribution among the two redox active type 1 (T1) Cu sites and the TNC. This shift in potential enables the intramolecular electron transfer (IET) from the T1 Cu to the native intermediate (NI) and accelerates the IET from the T1 Cu to the TNC, resulting in faster turnover in Cp catalysis.