Structural and functional study of rabbit muscle glycogenin

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Identification of critical residues of influenza neuraminidase in viral particle release

BACKGROUND: Influenza neuraminidase (NA) is essential for virus release from its host cells and it is one of the targets for structure-based antiviral drug design. RESULTS: In this report, we established a pseudoviral particle release assay to study NA function, which is based on lentiviral particles pseudotyped with influenza glycoproteins HA and NA as a surrogate system. Through an extensive molecular analysis, we sought to characterize important residues governing NA function. We identified five residues of NA, 234, 241, 257, 286 and 345, four of which (except 345) map away from the active site of NA when projected onto the three-dimensional structure of avian influenza H5N1 NA, and substitutions of these residues adversely affected the NA-mediated viral particle release, suggesting that these residues are critical for NA enzymatic activity. CONCLUSION: Through extensive chimeric and mutational analyses, we have identified several residues, which map away from the active site and are critical for NA function. These findings provide new insights into NA-mediated pseudoviral particle release and may have important implications in drug design and therapeutics against influenza infection

Analysis of hemagglutinin-mediated entry tropism of H5N1 avian influenza

<p>Abstract</p> <p>Background</p> <p>Avian influenza virus H5N1 is a major concern as a potential global pandemic. It is thought that multiple key events must take place before efficient human-to-human transmission of the virus occurs. The first step in overcoming host restriction is viral entry which is mediated by HA, responsible for both viral attachment and viral/host membrane fusion. HA binds to glycans-containing receptors with terminal sialic acid (SA). It has been shown that avian influenza viruses preferentially bind to α2,3-linked SAs, while human influenza A viruses exhibit a preference for α2,6-linked SAs. Thus it is believed the precise linkage of SAs on the target cells dictate host tropism of the viruses.</p> <p>Results</p> <p>We demonstrate that H5N1 HA/HIV pseudovirus can efficiently transduce several human cell lines including human lung cells. Interestingly, using a lectin binding assay we show that the presence of both α2,6-linked and α2,3-linked SAs on the target cells does not always correlate with efficient transduction. Further, HA substitutions of the residues implicated in switching SA-binding between avian and human species did not drastically affect HA-mediated transduction of the target cells or target cell binding.</p> <p>Conclusion</p> <p>Our results suggest that a host factor(s), which is yet to be identified, is required for H5N1 entry in the host cells.</p

PDlim2 Selectively Interacts with the PDZ Binding Motif of Highly Pathogenic Avian H5N1 Influenza A Virus NS1

The multi-functional NS1 protein of influenza A virus is a viral virulence determining factor. The last four residues at the C-terminus of NS1 constitute a type I PDZ domain binding motif (PBM). Avian influenza viruses currently in circulation carry an NS1 PBM with consensus sequence ESEV, whereas human influenza viruses bear an NS1 PBM with consensus sequence RSKV or RSEV. The PBM sequence of the influenza A virus NS1 is reported to contribute to high viral pathogenicity in animal studies. Here, we report the identification of PDlim2 as a novel binding target of the highly pathogenic avian influenza virus H5N1 strain with an NS1 PBM of ESEV (A/Chicken/Henan/12/2004/H5N1, HN12-NS1) by yeast two-hybrid screening. The interaction was confirmed by in vitro GST pull-down assays, as well as by in vivo mammalian two-hybrid assays and bimolecular fluorescence complementation assays. The binding was also confirmed to be mediated by the interaction of the PDlim2 PDZ domain with the NS1 PBM motif. Interestingly, our assays showed that PDlim2 bound specifically with HN12-NS1, but exhibited no binding to NS1 from a human influenza H1N1 virus bearing an RSEV PBM (A/Puerto Rico/8/34/H1N1, PR8-NS1). A crystal structure of the PDlim2 PDZ domain fused with the C-terminal hexapeptide from HN12-NS1, together with GST pull-down assays on PDlim2 mutants, reveals that residues Arg16 and Lys31 of PDlim2 are critical for the binding between PDlim2 and HN12-NS1. The identification of a selective binding target of HN12-NS1 (ESEV), but not PR8-NS1 (RSEV), enables us to propose a structural mechanism for the interaction between NS1 PBM and PDlim2 or other PDZ-containing proteins

Social Capital at Venture Capital Firms and Their Financial Performance in China

By using social network analysis, this paper studies the extent to which social capital drives performance in the Chinese venture capital (VC) market and explores the trend toward VC syndication in China. First, this paper proposes a hybrid model based on syndicated social networks and the latent-variable model, which describes the social capital at VC firms and builds relationships between social capital and performance at VC firms. Then, this paper builds three hypotheses about the relationships and test the hypotheses using our proposed model. Some numerical simulations are given to support the test results. Finally, this paper shows the correlations between social capital and financial performance at VC firms which are weak in China due to the lack of mature social capital links

Wideband 3-D Printed All-Metal Reflectarray With Notches for Low-Cost Millimeter-Wave Applications

In this paper, a 3-D printed all-metal reflectarray is presented for millimeter-wave applications. The array has sub-wavelength element spacing, so that the elements are non-resonant. A two-stage notch is etched at the top of the element, which provides multiple degrees of freedom for phase tuning. The phase variation range is more than 360&#x00B0; by changing the height and width of the first stage of the notch. Thanks to the non-resonant property and the two-stage notching, stable phase shift can be maintained in wide frequency range. A reflectarray with $20\times 20$ elements is fabricated by using 3-D printing technique, which has the merits of flexible construction, light weight and low cost. The simulated and measured results on radiation patterns and realized gain are highly consistent. The measured 1-dB gain bandwidth achieves 17.6&#x0025;, ranging from 31 GHz to 37 GHz. In the whole 1-dB gain bandwidth, the measured aperture efficiency is higher than 47.7&#x0025;, with a peak efficiency of 53.6&#x0025; at 31 GHz. The proposed reflectarray has no substrate loss and can provide high aperture efficiency in wide bandwidth

A Herpesvirus Virulence Factor Inhibits Dendritic Cell Maturation through Protein Phosphatase 1 and IκB Kinase▿

Dendritic cells are sentinels in innate and adaptive immunity. Upon virus infection, a complex program is in operation, which activates IκB kinase (IKK), a key regulator of inflammatory cytokines and costimulatory molecules. Here we show that the γ134.5 protein, a virulence factor of herpes simplex viruses, blocks Toll-like receptor-mediated dendritic cell maturation. While the wild-type virus inhibits the induction of major histocompatibility complex (MHC) class II, CD86, interleukin-6 (IL-6), and IL-12, the γ134.5-null mutant does not. Notably, γ134.5 works in the absence of any other viral proteins. When expressed in mammalian cells, including dendritic cells, γ134.5 associates with IKKα/β and inhibits NF-κB activation. This is mirrored by the inhibition of IKKα/β phosphorylation, p65/RelA phosphorylation, and nuclear translocation in response to lipopolysaccharide or poly(I:C) stimulation. Importantly, γ134.5 recruits both IKKα/β and protein phosphatase 1, forming a complex that dephosphorylates two serine residues within the catalytic domains of IκB kinase. The amino-terminal domain of γ134.5 interacts with IKKα/β, whereas the carboxyl-terminal domain binds to protein phosphatase 1. Deletions or mutations in either domain abolish the activity of γ134.5. These results suggest that the control of IκB kinase dephosphorylation by γ134.5 represents a critical viral mechanism to disrupt dendritic cell functions

An Herpesvirus Virulence Factor Inhibits Dendritic Cell Activation Through Protein Phosphatase 1 and IκB Kinase

Dendritic cells are sentinels in innate and adaptive immunity. Upon virus infection, a complex program is in operation, which activates I kappa B kinase (IKK), a key regulator of inflammatory cytokines and costimulatory molecules. Here we show that the gamma(1)34.5 protein, a virulence factor of herpes simplex viruses, blocks Toll-like receptor-mediated dendritic cell maturation. While the wild-type virus inhibits the induction of major histocompatibility complex (MHC) class II, CD86, interleukin-6 (IL-6), and IL-12, the gamma(1)34.5-null mutant does not. Notably, gamma(1)34.5 works in the absence of any other viral proteins. When expressed in mammalian cells, including dendritic cells, gamma(1)34.5 associates with IKK alpha/beta and inhibits NF-kappa B activation. This is mirrored by the inhibition of IKK alpha/beta phosphorylation, p65/RelA phosphorylation, and nuclear translocation in response to lipopolysaccharide or poly(I:C) stimulation. Importantly, gamma(1)34.5 recruits both IKK alpha/beta and protein phosphatase 1, forming a complex that dephosphorylates two serine residues within the catalytic domains of I kappa B kinase. The amino-terminal domain of gamma(1)34.5 interacts with IKK alpha/beta, whereas the carboxyl-terminal domain binds to protein phosphatase 1. Deletions or mutations in either domain abolish the activity of gamma(1)34.5. These results suggest that the control of I kappa B kinase dephosphorylation by gamma(1)34.5 represents a critical viral mechanism to disrupt dendritic cell functions