Identification of a Protein That Inhibits the Phosphorylated Form of Nitrate Reductase from Spinach (Spinacia oleracea) Leaves

The low-activity, phosphorylated form of nitrate reductase (NR) became activated during purification from spinach (Spinacia oleracea) leaves harvested in the dark. This activation resulted from its separation from an approximately 110-kd nitrate reductase inhibitor protein (NIP). Readdition of NIP inactivated the purified phosphorylated NR, but not the active dephosphorylated form of NR, indicating that the inactivation of NR requires its interaction with NIP as well as phosphorylation. Consistent with this hypothesis, NR that had been inactivated in vitro in the presence of NR kinase, ATP-Mg, and NIP could be reactivated either by dephosphorylation with protein phosphatase 2A or by dissociation of NIP from NR.     

The effect of HAART on humoral immune response in primary HIV-1 infected patients

The effect of Highly Active Antiretroviral Therapy (HAART) on binding and neutralizing antibody responses to human immunodeficiency virus type-1 (HIV-1) during primary and chronic infection was investigated. Seven patients HAART treated during primary infection, six HAART treated during chronic infection and five patients treated only with ZVD (Zidovudine) were analysed. HAART inhibited the development of anti env antibodies during primary infection. Administering HAART during primary infection usually did not substantially affect the development of weak neutralizing antibody responses against autologous virus. However, we demonstrated that very early treatment, during seroconversion, induce in some cases, a strong neutralizing antibodies against autologous virus. These results may be relevant for understanding how HAART may elicit a strong protective responses and may be useful in developing new strategies designed to achieve a long term control of the HIV infection.     

Structural basis of the interaction between integrin α6β4 and plectin at the hemidesmosomes

The interaction between the integrin α6β4 and plectin is essential for the assembly and stability of hemidesmosomes, which are junctional adhesion complexes that anchor epithelial cells to the basement membrane. We describe the crystal structure at 2.75 Å resolution of the primary α6β4–plectin complex, formed by the first pair of fibronectin type III domains and the N‐terminal region of the connecting segment of β4 and the actin‐binding domain of plectin. Two missense mutations in β4 (R1225H and R1281W) linked to nonlethal forms of epidermolysis bullosa prevent essential intermolecular contacts. We also present two structures at 1.75 and 2.05 Å resolution of the β4 moiety in the absence of plectin, which reveal a major rearrangement of the connecting segment of β4 on binding to plectin. This conformational switch is correlated with the way α6β4 promotes stable adhesion or cell migration and suggests an allosteric control of the integrin.     

Insulin receptor activation by proinsulin preserves synapses and vision in retinitis pigmentosa

Synaptic loss, neuronal death, and circuit remodeling are common features of central nervous system neurodegenerative disorders. Retinitis pigmentosa (RP), the leading cause of inherited blindness, is a group of retinal dystrophies characterized by photoreceptor dysfunction and death. The insulin receptor, a key controller of metabolism, also regulates neuronal survival and synaptic formation, maintenance, and activity. Indeed, deficient insulin receptor signaling has been implicated in several brain neurodegenerative pathologies. We present evidence linking impaired insulin receptor signaling with RP. We describe a selective decrease in the levels of the insulin receptor and its downstream effector phospho-S6 in retinal horizontal cell terminals in the rd10 mouse model of RP, as well as aberrant synapses between rod photoreceptors and the postsynaptic terminals of horizontal and bipolar cells. A gene therapy strategy to induce sustained proinsulin, the insulin precursor, production restored retinal insulin receptor signaling, by increasing S6 phosphorylation, without peripheral metabolic consequences. Moreover, proinsulin preserved photoreceptor synaptic connectivity and prolonged visual function in electroretinogram and optomotor tests. These findings point to a disease-modifying role of insulin receptor and support the therapeutic potential of proinsulin in retinitis pigmentosa.Subject terms: Neurodegeneration, Diseases     

Toxicity of familial ALS-linked SOD1 mutants from selective recruitment to spinal mitochondria

One cause of amyotrophic lateral sclerosis (ALS) is mutation in ubiquitously expressed copper/zinc superoxide dismutase (SOD1), but the mechanism of toxicity to motor neurons is unknown. Multiple disease-causing mutants, but not wild-type SOD1, are now demonstrated to be recruited to mitochondria, but only in affected tissues. This is independent of the copper chaperone for SOD1 and dismutase activity. Highly preferential association with spinal cord mitochondria is seen in human ALS for a mutant SOD1 that accumulates only to trace cytoplasmic levels. Despite variable proportions that are successfully imported, nearly constant amounts of SOD1 mutants and covalently damaged adducts of them accumulate as apparent import intermediates and/or are tightly aggregated or crosslinked onto integral membrane components on the cytoplasmic face of those mitochondria. These findings implicate damage from action of spinal cord-specific factors that recruit mutant SOD1 to spinal mitochondria as the basis for their selective toxicity in ALS.     

Translational and rotational motions of proteins in a protein crowded environment

Fluorescence correlation spectroscopy (FCS) was used to measure the translational diffusion of labeled apomyoglobin (tracer) in concentrated solutions of ribonuclease A and human serum albumin (crowders), as a quantitative model system of protein diffusive motions in crowded physiological environments. The ratio of the diffusion coefficient of the tracer protein in the protein crowded solutions and its diffusion coefficient in aqueous solution has been interpreted in terms of local apparent viscosities, a molecular parameter characteristic for each tracer-crowder system. In all protein solutions studied in this work, local translational viscosity values were larger than the solution bulk viscosity, and larger than rotational viscosities estimated for apomyoglobin in the same crowding solutions. Here we propose a method to estimate local apparent viscosities for the tracer translational and rotational diffusion directly from the bulk viscosity of the concentrated protein solutions. As a result of this study, the identification of protein species and the study of hydrodynamic changes and interactions in model crowded protein solutions by means of FCS and time-resolved fluorescence depolarization techniques may be expected to be greatly simplified.     

Studies of diurnal variations of nitrate reductase activity in barley leaves using various assay methods

The in vitro and various modifications of the in vivo assay for nitrate reductase have been compared in order to elucidate their usefulness in studies of diurnal variations of enzyme activity in barley leaves ( Hordeum vulgare L. cv. Herta). Generally, activity was low in the morning and increased rapidly during the first hours of the photoperiod. In the in vivo assay the leaf tissue was vacuum-infiltrated, whereafter either N₂ was bubbled through the assay buffer (anaerobic assay), or no N₂ was used (aerobic assay). Activity was 2–25 times higher in the anaerobic than in the aerobic assay. Anaerobiosis enhanced activity most during the dark period when the nitrate reductase level was low. Aerobic in vivo activity usually showed a more rapid decrease towards the end of the light period than did anaerobic activity. Addition of glucose and/or nitrate to the in vivo assay buffer usually stimulated activity more in the aerobic than in the anaerobic assay. In the morning, at the end of the dark period, these additives stimulated activity by 20–400% depending on growth and assay conditions. Later in the day stimulation was usually less, and even a slight inhibition was observed when only nitrate (0.1 M ) was added. The effect of these additives on the activity patterns determined was to dampen the oscillations. The additives were therefore not advantageous when testing diurnal variations. However, when the plants were grown under relatively poor light conditions it was necessary to add nitrate and glucose to the aerobic in vivo assay buffer since activity was otherwise too low to be measured. The in vitro assay gave about 5 times higher activity than the anaerobic in vivo assay. During the last part of the dark period in vivo activity (without glucose and KNO₃ in the assay buffer) decreased while in vitro activity remained constant.     

Antibacterial activity of an oligosaccharide of native Paecilomyces sp. and its aminoglycosylated derivative

This study reports the antibacterial activity of an oligosaccharide, prepared by partial acid hydrolysis of a native Paecilomyces sp. exopolysaccharide, and of its aminoglycosylated derivative, prepared by reductive alkylation of the oligosaccharide, against E. coli and S. aureus.