Cellular requirements for iron-sulfur cluster insertion into the antiviral radical SAM protein viperin

Viperin (RSAD2) is an interferon-stimulated antiviral protein that belongs to the radical S-adenosylmethionine (SAM) enzyme family. Viperin's iron-sulfur (Fe/S) cluster is critical for its antiviral activity against many different viruses. CIA1 (CIAO1), an essential component of the cytosolic iron-sulfur protein assembly (CIA) machinery, is crucial for Fe/S cluster insertion into viperin and hence for viperin's antiviral activity. In the CIA pathway, CIA1 cooperates with CIA2A, CIA2B, and MMS19 targeting factors to form various complexes that mediate the dedicated maturation of specific Fe/S recipient proteins. To date, however, the mechanisms of how viperin acquires its radical SAM Fe/S cluster to gain antiviral activity are poorly understood. Using co-immunoprecipitation and ⁵⁵Fe-radiolabeling experiments, we therefore studied the roles of CIA2A, CIA2B, and MMS19 for Fe/S cluster insertion. CIA2B and MMS19 physically interacted with the C terminus of viperin and used CIA1 as the primary viperin-interacting protein. In contrast, CIA2A bound to viperin's N terminus in a CIA1-, CIA2B-, and MMS19-independent fashion. Of note, the observed interaction of both CIA2 isoforms with a single Fe/S target protein is unprecedented in the CIA pathway. ⁵⁵Fe-radiolabeling experiments with human cells depleted of CIA1, CIA2A, CIA2B, or MMS19 revealed that CIA1, but none of the other CIA factors, is predominantly required for ⁵⁵Fe/S cluster incorporation into viperin. Collectively, viperin maturation represents a novel CIA pathway with a minimal requirement of the CIA-targeting factors and represents a new paradigm for the insertion of the Fe/S cofactor into a radical SAM protein.

Molecular thermodynamics of metabolism: quantum thermochemical calculations for key metabolites

The present work is the first of a series of papers aiming at a coherent and unified development of the thermodynamics of metabolism and the rationalization of feasibility analysis of metabolic pathways. The focus in this part is on high-level quantum chemical calculations of the thermochemical quantities of relatively heavy metabolites such as amino acids/oligopeptides, nucleosides, saccharides and their derivatives in the ideal gas state. The results of this study will be combined with the corresponding hydration/solvation results in subsequent parts of this work in order to derive the desired thermochemical quantities in aqueous solutions. The above metabolites exist in a vast conformational/isomerization space including rotational conformers, tautomers or anomers exhibiting often multiple or cooperative intramolecular hydrogen bonding. We examine the challenges posed by these features for the reliable estimation of thermochemical quantities. We discuss conformer search, conformer distribution and averaging processes. We further consider neutral metabolites as well as protonated and deprotonated metabolites. In addition to the traditional presentation of gas-phase acidities, basicities and proton affinities, we also examine heats and free energies of ionic species. We obtain simple linear relations between the thermochemical quantities of ions and the formation quantities of their neutral counterparts. Furthermore, we compare our calculations with reliable experimental measurements and predictive calculations from the literature, when available. Finally, we discuss the next steps and perspectives for this work.

Aetiology of Acute Respiratory Tract Infections in Hospitalised Children in Cyprus

In order to improve clinical management and prevention of viral infections in hospitalised children improved etiological insight is needed. The aim of the present study was to assess the spectrum of respiratory viral pathogens in children admitted to hospital with acute respiratory tract infections in Cyprus. For this purpose nasopharyngeal swab samples from 424 children less than 12 years of age with acute respiratory tract infections were collected over three epidemic seasons and were analysed for the presence of the most common 15 respiratory viruses. A viral pathogen was identified in 86% of the samples, with multiple infections being observed in almost 20% of the samples. The most frequently detected viruses were RSV (30.4%) and Rhinovirus (27.4%). RSV exhibited a clear seasonality with marked peaks in January/February, while rhinovirus infections did not exhibit a pronounced seasonality being detected almost throughout the year. While RSV and PIV3 incidence decreased significantly with age, the opposite was observed for influenza A and B as well as adenovirus infections. The data presented expand our understanding of the epidemiology of viral respiratory tract infections in Cypriot children and will be helpful to the clinicians and researchers interested in the treatment and control of viral respiratory tract infections.

Molecular thermodynamics of metabolism: hydration quantities and the equation-of-state approach

Comprehensive and consistent calculations of hydration quantities, including conformational contributions.

The human adenylate kinase 9 is a nucleoside mono- and diphosphate kinase

Adenylate kinases regulate adenine nucleotide levels and are present in different intracellular compartments. These enzymes also participate in the activation of pharmacologically active nucleoside and nucleotide analogs. We have in the present study identified the ninth isoform of the adenylate kinase family of enzymes and accordingly named the protein adenylate kinase 9 (AK9). Initially a full-length cDNA of a hypothetical protein containing a predicted adenylate kinase domain was identified and subsequently cloned and expressed in Escherichia coli. The substrate specificity of the recombinant protein showed that the enzyme catalyzed the phosphorylation of AMP, dAMP, CMP and dCMP with ATP as phosphate donor, while only AMP and CMP were phosphorylated when GTP was the phosphate donor. The kinetic parameters of AK9 were determined for AMP, dAMP and CMP with ATP as phosphate donor. Interestingly, in addition to the diphosphate products, a nucleoside diphosphate kinase (NDPK) activity was also present with subsequent triphosphates formed. With ATP or GTP as phosphate donor it was possible to detect the production of ATP, CTP, GTP, UTP, dATP, dCTP, dGTP and TTP as enzymatic products from the corresponding diphosphate substrates. A number of previously characterized adenylate kinases were also tested and found to possess a broad phosphotransferase activity similar to AK9. These enzymes are accordingly suggested to be regarded as nucleoside mono- and diphosphate kinases with catalytic activities possibly determined by local substrate concentrations.

Evidence of an intact N-terminal translocation sequence of human mitochondrial adenylate kinase 4

Adenylate kinases are abundant nucleoside monophosphate kinases, which catalyze the phosphorylation of AMP by using ATP or GTP as phosphate donors. A previously cloned cDNA was named adenylate kinase 4 (AK4) based on its sequence similarity with known AKs but with no confirmed AK enzyme activity. In the present study the AK4 cDNA was expressed in Escherichia coli and the substrate specificity and kinetic properties of the recombinant protein were characterized. The enzyme catalyzed the phosphorylation of AMP, dAMP, CMP and dCMP with ATP or GTP as phosphate donors and AK4 also phosphorylated AMP with UTP as phosphate donor. The kinetic parameters of the enzyme were determined for AMP and dAMP with ATP as phosphate donor and for AMP with GTP as phosphate donor. AK4 showed its highest efficiency when phosphorylating AMP with GTP and a slightly lower efficiency for the phosphorylation of AMP with ATP. Among the three reactions for which kinetics were performed, dAMP was the poorest substrate. The AK4 mitochondrial localization was confirmed by expression of AK4 as a fusion protein with GFP in HeLa cells. The mitochondrial import sequence was shown to be located within the first N-terminal 11 amino acid residues, very close to the ATP-binding region of the enzyme. Import analysis suggested that the mitochondrial import sequence was not cleaved and thus the enzyme retained its activity upon entering the mitochondria. Site directed mutagenesis of amino acids Lys 4 and Arg 7 showed that these two residues were essential for mitochondrial import.

Thermal and colloidal behavior of amine-treated clays: the role of amphiphilic organic cation concentration

The modification of sodium montmorillonite (NaMMT) through the insertion of amphiphilic hexadecylammonium cations into the clay's interlayer spaces has been studied. Alkylammonium concentrations equivalent to 0.15-3.00 times the cation exchange capacity of the clay were used. The conformation of the surfactant cations in the confined space of the silicate galleries was investigated by X-ray diffraction analysis and scanning electron microscopy, while the organoclay's thermal stability was examined by thermogravimetric analysis. The clay's surface properties induced by the ion-exchange process were followed by measurements of the mineral's zeta potential as a function of pH and surfactant concentration, while the coagulation rates of organoclay suspensions in water and in chloroform were examined using dynamic light scattering. All the results are consistent with showing that the overall characteristics and thus the behavior of the modified MMT particles strongly depend on the alkylammonium surfactant concentration used in the modification process. This, however, has very important implications for any attempt to incorporate the organomodified MMT particles into different media for various applications such as polymer nanocomposite preparation.

Formation of hydroxyapatite/biopolymer biomaterials. I. Microporous composites from solidified emulsions

Microporous materials of controlled pore size were prepared by means of a three-step process involving in situ hydrochemical preparation of a hydroxyapatite-sodium caseinate (HAp-Cas) composite material into a Cas-stabilized oil-in-water emulsion, subsequent concentration and drying of the composite-emulsion, and removal of the oil by means of supercritical carbon dioxide extraction. The resulting composite materials were found to contain micron-sized pores in the space previously occupied by the oil droplets. In order to elucidate the structure of the resulting porous product, its Cas-HAp composition was studied in the corresponding nonporous composite material. In nonporous samples, a protein assay by means of visible spectroscopy suggested equilibrium between the Cas that was trapped in the composite structure and the Cas that remained in solution after precipitation. This observation was confirmed by separate thermogravimetric analysis and Fourier transform IR spectroscopy measurements.

Thermodynamics of Alkoxyethanol + Alkane Mixtures

New spectroscopic data are reported for the intermolecular and intramolecular hydrogen bonding in 2-methoxyethanol +