SYNTHESIS AND STRUCTURE DETERMINATION OF A NUCLEOSIDEDERIVED NEW HETEROCYCLIC SYSTEM: 8H,10H,15b(S)-2,3,6,7-TETRAHYDRO-1,5,3-DIOXAZEPINO[3,2-c]INDOLO[3,2-g]PTERIDINE-7-ONE

Abstract

Condensation of 5-aminocytidine with N-methylisatin yielded a new heterocyclic system, 8H,10H,15b(S)-2,3,6,7-tetrahydro-1,5,3-dioxazepino[3,2-c]indolo[3,2-g]pteridine-7- one. The assignment of S configuration at position 15b, which is generated as a result of the nucleophilic attack of the 5′-hydroxy of the ribosyl moiety at the position 6 of the cytosine base, is discussed.     

Mechanistic Similarities Between Thymidylate Synthase and IMP Dehydrogenase: A Common Strategy of Catalysis

Abstract

Thymidylate synthase (TS) and inosine 5′-monophosphate dehydrogenase (IMPDH) are important targets of drug action and development. The two enzymes bear no structural resemblance to each other and they catalyze fundamentally different chemical reactions     

Plasma Levels of Trace Elements Have an Implication on Interferon Treatment of Children with Chronic Hepatitis B Infection

This study evaluated the plasma levels of trace elements in children with chronic hepatitis B virus (HBV) infection and assessed whether they can be a factor that affects the response to interferon alpha (IFN-α) treatment. The study included 35 cases (ten girls, 25 boys) aged 3–13 years with chronic HBV infection and the control group. Plasma levels of copper (Cu), manganese (Mn), molybdenum (Mo), selenium (Se), and zinc (Zn) were measured before IFN-α treatment and biochemical, virological, and histopathologic response to treatment were assessed. Children were followed for at least 15 months. Although plasma Cu levels showed no difference between the groups, Mn, Mo, Se, and Zn levels were significantly lower in the study group before treatment. Fourteen cases (40%) showed biochemical response; 17 (48.6%) showed virological response; 16 (47.6%) showed histopathologic response, and ten (28.6%) showed response according to all three parameters. Plasma Cu and Mn levels of patients with triple response showed no difference; but Mo, Se, and Zn levels were significantly lower (p?<?0.001) in the study group. No difference was observed between responders and nonresponders (p?>?0.05). Plasma levels of Mn, Mo, Se, and Zn are lower in children with chronic HBV infection compared to healthy children. The pretreatment levels of these elements did not show difference between responders and nonresponders to IFN-α.     

AQP0-LTR of the Cat Fr mouse alters water permeability and calcium regulation of wild type AQP0

Aquaporin 0 (AQP0) is the major intrinsic protein of the lens and its water permeability can be modulated by changes in pH and Ca2+. The Cataract Fraser (Cat Fr) mouse accumulates an aberrant AQP0 (AQP0-LTR) in sub-cellular compartments resulting in a congenital cataract. We investigated the interference of AQP0-LTR with normal function of AQP0 in three systems. First, we created a transgenic mouse expressing AQP0 and AQP0-LTR in the lens. Expression of AQP0 did not prevent the congenital cataract but improved the size and transparency of the lens. Second, we measured water permeability of AQP0 co-expressed with AQP0-LTR in Xenopus oocytes. A low expression level of AQP0-LTR decreased the water permeability of AQP0, and a high expression level eliminated its calcium regulation. Third, we studied trafficking of AQP0 and AQP0-LTR in transfected lens epithelial cells. At low expression level, AQP0-LTR migrated with AQP0 toward the cell membrane, but at high expression level, it accumulated in sub-cellular compartments. The deleterious effect of AQP0-LTR on lens development may be explained by lowering water permeability and abolishing calcium regulation of AQP0. This study provides the first evidence that calcium regulation of AQP0 water permeability may be crucial for maintaining normal lens homeostasis and development.     

Disorder and sequence repeats in hub proteins and their implications for network evolution

Protein interaction networks display approximate scale-free topology, in which hub proteins that interact with a large number of other proteins determine the overall organization of the network. In this study, we aim to determine whether hubs are distinguishable from other networked proteins by specific sequence features. Proteins of different connectednesses were compared in the interaction networks of Saccharomyces cerevisiae, Drosophila melanogaster, Caenorhabditis elegans, and Homo sapienswith respect to the distribution of predicted structural disorder, sequence repeats, low complexity regions, and chain length. Highly connected proteins ("hub proteins") contained significantly more of, and greater proportion of, these sequence features and tended to be longer overall as compared to less connected proteins. These sequence features provide two different functional means for realizing multiple interactions: (1) extended interaction surface and (2) flexibility and adaptability, providing a mechanism for the same region to bind distinct partners. Our view contradicts the prevailing view that scaling in protein interactomes arose from gene duplication and preferential attachment of equivalent proteins. We propose an alternative evolutionary network specialization process, in which certain components of the protein interactome improved their fitness for binding by becoming longer or accruing regions of disorder and/or internal repeats and have therefore become specialized in network organization.     

Differences and similarities in viral life cycle progression and host cell physiology after infection of human dendritic cells with modified vaccinia virus Ankara and vaccinia virus

Modified vaccinia virus Ankara (MVA) is an attenuated strain of vaccinia virus (VV) that has attracted significant attention as a candidate viral vector vaccine for immunization against infectious diseases and treatment of malignancies. Although MVA is unable to replicate in most nonavian cells, vaccination with MVA elicits immune responses that approximate those seen after the administration of replication-competent strains of VV. However, the mechanisms by which these viruses elicit immune responses and the determinants of their relative immunogenicity are incompletely understood. Studying the interactions of VV and MVA with cells of the human immune system may elucidate these mechanisms, as well as provide a rational basis for the further enhancement of the immunogenicity of recombinant MVA vectors. Toward this end, we investigated the consequences of MVA or VV infection of human dendritic cells (DCs), key professional antigen-presenting cells essential for the generation of immune responses. We determined that a block to the formation of intracellular viral replication centers results in abortive infection of DCs with both VV and MVA. MVA inhibited cellular protein synthesis more rapidly than VV and displayed a distinct pattern of viral protein expression in infected DCs. MVA also induced apoptosis in DCs more rapidly than VV, and DC apoptosis after MVA infection was associated with an accelerated decline in the levels of intracellular Bcl-2 and Bcl-X(L). These findings suggest that antigen presentation pathways may contribute differentially to the immunogenicity of VV and MVA and that targeted modifications of virus-induced DC apoptosis may further increase the immunogenicity of MVA-vectored vaccines.     

Structural disorder serves as a weak signal for intracellular protein degradation

Targeted turnover of proteins is a key element in the regulation of practically all basic cellular processes. The underlying physicochemical and/or sequential signals, however, are not fully understood. This issue is particularly pertinent in light of the recent recognition that intrinsically unstructured/disordered proteins, common in eukaryotic cells, are extremely susceptible to proteolytic degradation in vitro. The in vivo half-lives of proteins were determined recently in a high-throughput study encompassing the entire yeast proteome; here we examine whether these half-lives correlate with the presence of classical degradation motifs (PEST region, destruction-box, KEN-box, or the N-terminal residue) or with various physicochemical characteristics, such as the size of the protein, the degree of structural disorder, or the presence of low-complexity regions. Our principal finding is that, in general, the half-life of a protein does not depend on the presence of degradation signals within its sequence, even of ubiquitination sites, but correlates mainly with the length of its polypeptide chain and with various measures of structural disorder. Two distinct modes of involvement of disorder in degradation are proposed. Susceptibility to degradation of longer proteins, containing larger numbers of residues in conformational disorder, suggests an extensive function, whereby the effect of disorder can be ascribed to its mere physical presence. However, after normalization for protein length, the only signal that correlates with half-life is disorder, which indicates that it also acts in an intensive manner, that is, as a specific signal, perhaps in conjunction with the recognition of classical degradation motifs. The significance of correlation is rather low; thus protein degradation is not determined by a single characteristic, but is a multi-factorial process that shows large protein-to-protein variations. Protein disorder, nevertheless, plays a key signalling role in many cases.