HIV-host interactions: vital to the virus and key to its inhibition

Much progress has been made in recent years in the investigation of the interplay between HIV-1 and its host cells. Most of these interactions are complex and have not yet been fully unraveled. Nevertheless, current knowledge on the molecular interactions between HIV and host-cell factors has substantially broadened our understanding of the viral life cycle and opened new investigative areas for drug intervention.     

Motor-cargo interactions: the key to transport specificity

Eukaryotic cells organize their cytoplasm by moving different organelles and macromolecular complexes along microtubules and actin filaments. These movements are powered by numerous motor proteins that must recognize their respective cargoes in order to function. Recently, several proteins that interact with motors have been identified by yeast two-hybrid and biochemical analyses, and their roles in transport are now being elucidated. In several cases, analysis of the binding partners helped to identify new transport pathways, new types of cargo, and transport regulated at the level of motor-cargo binding. We discuss here how different motors of the kinesin, dynein and myosin families recognize their cargo and how motor-cargo interactions are regulated.     

Metabolism as a key to histone deacetylase inhibition

There is growing interest in the epigenetic mechanisms that are dysregulated in cancer and other human pathologies. Under this broad umbrella, modulators of histone deacetylase (HDAC) activity have gained interest as both cancer chemopreventive and therapeutic agents. Of the first generation, FDA-approved HDAC inhibitors to have progressed to clinical trials, vorinostat represents a "direct acting" compound with structural features suitable for docking into the HDAC pocket, whereas romidepsin can be considered a prodrug that undergoes reductive metabolism to generate the active intermediate (a zinc-binding thiol). It is now evident that other agents, including those in the human diet, can be converted by metabolism to intermediates that affect HDAC activity. Examples are cited of short-chain fatty acids, seleno-α-keto acids, small molecule thiols, mercapturic acid metabolites, indoles, and polyphenols. The findings are discussed in the context of putative endogenous HDAC inhibitors generated by intermediary metabolism (e.g. pyruvate), the yin-yang of HDAC inhibition versus HDAC activation, and the screening assays that might be most appropriate for discovery of novel HDAC inhibitors in the future.     

Uncovering the mystery of Ebola virus entry: Lock and key

正How Ebola virus(EBOV)enters a host cell remains intriguingly mysterious to the public.Recently,a study led by George F Gao and his colleagues has unveiled how the primed glycoprotein on the envelope of EBOV binds to its endosomal receptor Niemann-Pick C1(NPC1)molecule during the process of virus membrane fusion with the host cells,an essential step for viral entry(Wang et al.,2016).This fine resolution of the viral glycoprotein with NPC1 at the atomic level sheds light on the development of therapeutic inhibitors against EBOV infection.     

Molecular characterization of key diphtheria toxin:receptor interactions

The major amino acids necessary for diphtheria toxin (DT) binding to its receptor have been identified previously. Studies by W. H. Shen et al. (J. Biol. Chem. 269, 29077-29084, 1994) and by J. H. Cha et al. (Mol. Microbiol. 29 (5), 1275-1284, 1998) suggested that the positively charged nature of the single amino acid residue, (516)Lys of DT, is crucial for binding to the DT receptor, whereas the negatively charged (141)Glu of the DT receptor is the most important residue for toxin binding. Here, we hypothesize that key interactions occur between these two oppositely charged amino acid residues. Reciprocal substitution of the residues at these positions between the toxin and the receptor was performed, which resulted in a partial reconstitution of the toxin:receptor interaction. This study provides the first biological data that characterizes the specific interaction of these two key residues with each other and also the additional interactions between other positively charged residues of DT and (141)Glu of the DT receptor.     

Varicella-zoster virus: molecular virology and virus-host interactions

Cosmid-based mutagenesis and methods to examine varicella-zoster virus (VZV) tropism for differentiated human cells in vivo provide new information about molecular mechanisms of VZV infection. How specific VZV gene products contribute to viral replication has been further defined, and effects of VZV on expression of cellular genes have been demonstrated.     

Host thermal biology: the key to understanding host–pathogen interactions and microbial pest control?

1 The role of pathogens in insect population dynamics remains poorly understood and their performance in biological control is erratic. Here we identify that temperature and host thermal behaviour, both the active interaction with environmental temperature and solar radiation via thermoregulation and the passive interception of these factors by thermal generalists, are central to understanding host–pathogen interactions. 2 We demonstrate that pathogenicity, the latent period of infection and host recovery rate can all vary dramatically across and between seasons due to thermal biology of the host and changes in environmental temperature. 3 Such effects have not been thoroughly explored in any previous investigations but may have major implications for disease dynamics in insects and possibly in ectotherms in general, and for development of effective biopesticides.     

Asymmetric ATP binding and hydrolysis activity of the Thermus aquaticus MutS dimer is key to modulation of its interactions with mismatched DNA

Prokaryotic MutS and eukaryotic Msh proteins recognize base pair mismatches and insertions or deletions in DNA and initiate mismatch repair. These proteins function as dimers (and perhaps higher order oligomers) and possess an ATPase activity that is essential for DNA repair. Previous studies of Escherichia coli MutS and eukaryotic Msh2-Msh6 proteins have revealed asymmetry within the dimer with respect to both DNA binding and ATPase activities. We have found the Thermus aquaticus MutS protein amenable to detailed investigation of the nature and role of this asymmetry. Here, we show that (a) in a MutS dimer one subunit (S1) binds nucleotide with high affinity and the other (S2) with 10-fold weaker affinity, (b) S1 hydrolyzes ATP rapidly while S2 hydrolyzes ATP at a 30-50-fold slower rate, (c) mismatched DNA binding to MutS inhibits ATP hydrolysis at S1 but slow hydrolysis continues at S2, and (d) interaction between mismatched DNA and MutS is weakened when both subunits are occupied by ATP but remains stable when S1 is occupied by ATP and S2 by ADP. These results reveal key MutS species in the ATPase pathway; S1(ADP)-S2(ATP) is formed preferentially in the absence of DNA or in the presence of fully matched DNA, while S1(ATP)-S2(ATP) and S1(ATP)-S2(ADP) are formed preferentially in the presence of mismatched DNA. These MutS species exhibit differences in interaction with mismatched DNA that are likely important for the mechanism of MutS action in DNA repair.     

Structural studies on AIPL1 and its functional interactions with NUB1 to identify key interacting residues in LCA4

Leber congenital amaurosis (LCA) is an autosomal recessive disorder that causes visual impairment in children due to fifteen different gene mutations. Of these, mutations in Aryl-Hydrocarbon Receptor Interacting Protein-like 1 (AIPL1) cause the most severe form of LCA (LCA4) leading to the degeneration of photoreceptor cells. NEDD8 Ultimate Buster 1 (NUB1), a protein that regulates cell cycle progression, interacts with AIPL1 to prevent the over expression of NUB1. In the case of over expression, cell cycle progression is disrupted and may lead to LCA. The studies on interactions between these two proteins will aid in identifying potential modulators for this condition. Since no three-dimensional structure is currently available for these two proteins, in this study we predicted the structures of these two proteins by molecular modelling methods. Moreover, we also modelled the three proven significant mutant forms of AIPL1 spanning the tetratricopeptide domain. Finally, both the modelled wild and mutant structures of AIPL1 (A197P, C239R and G262S) were computationally docked to NUB1, so as to map the potential molecular interactions. This is the first study on modelling the structure–function relationship of AIPL1–NUB1 interactions which shall aid in discovery of novel therapeutic agents.     

Examination of the folding pathway of the antigenomic hepatitis delta virus ribozyme reveals key interactions of the L3 loop

With the goal of gaining insight into the tertiary structure of the hepatitis delta virus ribozyme, cross-linking experiments using 4-thiouridine residues introduced in either the 5'-end portion of the substrate, or at seven strategic positions within the ribozyme, were performed. Mapping of the newly formed covalent bonds in cross-linked species obtained under various conditions, as well as using several mutated ribozymes, permitted monitoring of the formation of the ribozyme-substrate complex as the ribozyme proceeded along the folding pathway. In order to aid visualization of the tertiary structure transformation, an in silico animation of the "on" folding pathway was developed. In combination with those of the cleavage assays of structured substrates, these data shed light on the key contribution of the L3 loop in the formation of an active tertiary complex.     

Search for additional influenza virus to cell interactions

Sialyl oligosaccharides have long been considered to be the sole receptors for influenza virus. However, according to [1] some viruses are able to grow in sialic-free MDCK cells. Here we attempted to reveal a possible second, non-sialic receptor, hypothesizing the involvement of additional carbohydrate lectin recognition in influenza virus reception process, first of all in situations when a lectin of the host cell could recognize the viral carbohydrate ligand. We tested the presence of galactose- and sialic acid-binding lectins, as well as mannoside- and sulfo-N-acetyllactosamine-recognizing properties of MDCK and Vero cells using polyacrylamide neoglycoconjugates and antibodies. MDCK cells bind galactoside probes stronger than Vero cells, whereas Vero cells bind preferentially sialoside, mannoside and various sulfo-oligosaccharide probes. The probing of viruses with the neoglycoconjugates revealed specific 6′-HSO ₃ LacNAc (but not other sulfated oligosaccharides) binding property of A and B human strains. Affinity of 6′-HSO ₃ LacNAc probe was comparable with affinity of 6′-SiaLac probe but the binding was not inhibited by the sialooligosaccharide.     

Ezrin, Radixin and Moesin: key regulators of membrane-cortex interactions and signaling

The cell cortex serves as a critical nexus between the extracellular environment/cell membrane and the underlying cytoskeleton and cytoplasm. In many cells, the cell cortex is organized and maintained by the Ezrin, Radixin and Moesin (ERM) proteins, which have the ability to interact with both the plasma membrane and filamentous actin. Although this membrane-cytoskeletal linkage function is critical to stability of the cell cortex, recent studies indicate that this is only a part of what ERMs do in many cells. In addition to their role in binding filamentous actin, ERMs regulate signaling pathways through their ability to bind transmembrane receptors and link them to downstream signaling components. In this review we discuss recent evidence in a variety of cells indicating that ERMs serve as scaffolds to facilitate efficient signal transduction on the cytoplasmic face of the plasma membrane.     

Lipid-protein interactions: NMR study of melittin and its binding to lysophosphatidylcholine

Proton NMR of melittin differs according to the association state of the peptide in the monomer or tetramer. Melittin interacts with lysophosphatidylcholine micelles, whatever the association state of melittin; well resolved superimposed spectra from both components for all the lipid to peptide molar ratios are observed. Within the complexes, local mobility and fast exchange occurs. On binding concomitant shifts on Trp₁₉ indole lines and on the aliphatic CH₂ protons of the lipids are detected. The lipid perturbation is maximum for methylene groups in α and β of the ester bond, this could allow positionning of Trp₁₉ in the hydrophobic core of the lipids.