Selective inhibition of herpes simplex virus type-1 uracil-DNA glycosylase by designed substrate analogs

Cytosine deamination and the misincorporation of 2'-dUrd into DNA during replication result in the presence of uracil in DNA. Uracil-DNA glycosylases (UDGs) initiate the excision repair of this aberrant base by catalyzing the hydrolysis of the N-glycosidic bond. UDGs are expressed by nearly all known organisms, including some viruses, in which the functional role of the UDG protein remains unresolved. This issue could in principle be addressed by the availability of designed synthetic inhibitors that target the viral UDG without affecting the endogenous human UDG. Here, we report that double-stranded and single-stranded oligonucleotides incorporating either of two dUrd analogs tightly bind and inhibit the activity of herpes simplex virus type-1 (HSV-1) UDG. Both inhibitors are exquisitely specific for the HSV-1 UDG over the human UDG. These inhibitors should prove useful in structural studies aimed at understanding substrate recognition and catalysis by UDGs, as well as in elucidating the biologic role of UDGs in the life cycle of herpesviruses.     

Role of actin cytoskeleton in dendritic spine morphogenesis

Dendritic spines are the postsynaptic receptive regions of most excitatory synapses, and their morphological plasticity play a pivotal role in higher brain functions, such as learning and memory. The dynamics of spine morphology is due to the actin cytoskeleton concentrated highly in spines. Filopodia, which are thin and headless protrusions, are thought to be precursors of dendritic spines. Drebrin, a spine-resident side-binding protein of filamentous actin (F-actin), is responsible for recruiting F-actin and PSD-95 into filopodia, and is suggested to govern spine morphogenesis. Interestingly, some recent studies on neurological disorders accompanied by cognitive deficits suggested that the loss of drebrin from dendritic spines is a common pathognomonic feature of synaptic dysfunction. In this review, to understand the importance of actin-binding proteins in spine morphogenesis, we first outline the well-established knowledge pertaining to the actin cytoskeleton in non-neuronal cells, such as the mechanism of regulation by small GTPases, the equilibrium between globular actin (G-actin) and F-actin, and the distinct roles of various actin-binding proteins. Then, we review the dynamic changes in the localization of drebrin during synaptogenesis and in response to glutamate receptor activation. Because side-binding proteins are located upstream of the regulatory pathway for actin organization via other actin-binding proteins, we discuss the significance of drebrin in the regulatory mechanism of spine morphology through the reorganization of the actin cytoskeleton. In addition, we discuss the possible involvement of an actin-myosin interaction in the morphological plasticity of spines.     

Solid-phase synthesis of biologically active fragment 29-111 of rat prothymosin alpha

Rat prothymosin alpha fragment 29-111, an 83-residue polypeptide corresponding to desthymosin alpha 1-prothymosin alpha, has been synthesized by a solid-phase method. Hydrogen fluoride was used to deprotect and cleave the peptide from the resin. The crude product was purified by gel-filtration, ion-exchange chromatography and high-performance liquid chromatography. A 3.2-mg sample of a ca. 96% pure peptide was finally obtained. The overall yield of the synthesis was less than 1%. An increase of E-rosette-forming lymphocytes was obtained after incubation of peripheral blood from uremic patients with the synthetic prothymosin alpha fragment 29-111. The restoring effect of the synthetic prothymosin alpha fragment 29-111 was greater than that of our synthetic thymosin alpha 1.     

Synthesis of deacetylthymosin beta 11 and its effect on the impaired T-lymphocytes of a uremic patient with common variable immunodeficiency

The untetracontapeptide corresponding to the entire amino acid sequence of deacetylthymosin beta 11 was synthesized by assembling six peptide fragments via the azide followed by deprotection with 1 M trifluoromethanesulfonic acid-thioanisole in trifluoroacetic acid in the presence of dimethylselenide. The synthetic peptide was tested for its effect on the impaired blastogenic response of phytohemagglutinin-stimulated T-lymphocytes of a uremic patient with common variable immunodeficiency. The synthetic peptide had some restoring activity on the impaired blastogenic response of T-lymphocytes in the one patient tested.     

Herbivorous animals can mitigate unfavourable ratios of energy and material supplies by enhancing nutrient recycling

Recent evidence shows that high supply ratios of light and nutrients limit planktonic herbivore growth by lowering the nutritional quality of algae. Over longer time scales, however, grazers may ameliorate this effect by their impact on nutrient cycling. We examine this possibility using two species of the herbivorous zooplankter Daphnia and its algal prey under different light intensities and low phosphorus supply in laboratory microcosms. At high light, Daphnia biomass was limited for a substantial period because of low P content of algal cells. However, a gradual increase in Daphnia density eventually improved food quality through grazing and nutrient cycling and via a novel process involving positive density dependence. Competitive exclusion of one of the two Daphnia species occurred under low light but not under high light when algae were nutritionally unsuitable. Such stoichiometrically mediated interactions among herbivorous animals may represent important mechanisms that affect community structure and material flows in ecosystems.