The NS1 protein of influenza B virus binds 5'-triphosphorylated dsRNA to suppress RIG-I activation and the host antiviral response.

Influenza A and B viruses overcome the host antiviral response to cause a contagious and often severe human respiratory disease. Here, integrative structural biology and biochemistry studies on non-structural protein 1 of influenza B virus (NS1B) reveal a previously unrecognized viral mechanism for innate immune evasion. Conserved basic groups of its C-terminal domain (NS1B-CTD) bind 5'triphosphorylated double-stranded RNA (5'-ppp-dsRNA), the primary pathogen-associated feature that activates the host retinoic acid-inducible gene I protein (RIG-I) to initiate interferon synthesis and the cellular antiviral response.

Structure Determination of Challenging Protein-Peptide Complexes Combining NMR Chemical Shift Data and Molecular Dynamics Simulations.

Intrinsically disordered regions of proteins often mediate important protein-protein interactions. However, the folding-upon-binding nature of many polypeptide-protein interactions limits the ability of modeling tools to predict the three-dimensional structures of such complexes. To address this problem, we have taken a tandem approach combining NMR chemical shift data and molecular simulations to determine the structures of peptide-protein complexes.

A common binding motif in the ET domain of BRD3 forms polymorphic structural interfaces with host and viral proteins.

The extraterminal (ET) domain of BRD3 is conserved among BET proteins (BRD2, BRD3, BRD4), interacting with multiple host and viral protein-protein networks. Solution NMR structures of complexes formed between the BRD3 ET domain and either the 79-residue murine leukemia virus integrase (IN) C-terminal domain (IN) or its 22-residue IN tail peptide (IN) alone reveal similar intermolecular three-stranded β-sheet formations. N relaxation studies reveal a 10-residue linker region (IN) tethering the SH3 domain (IN) to the ET-binding motif (IN):ET complex.

A double-stranded RNA platform is required for the interaction between a host restriction factor and the NS1 protein of influenza A virus.

Influenza A viruses cause widespread human respiratory disease. The viral multifunctional NS1 protein inhibits host antiviral responses. This inhibition results from the binding of specific cellular antiviral proteins at various positions on the NS1 protein.

NMR characterization of HtpG, the E. coli Hsp90, using sparse labeling with C-methyl alanine.

A strategy for acquiring structural information from sparsely isotopically labeled large proteins is illustrated with an application to the E. coli heat-shock protein, HtpG (high temperature protein G), a 145 kDa dimer. It uses C-alanine methyl labeling in a perdeuterated background to take advantage of the sensitivity and resolution of Methyl-TROSY spectra, as well as the backbone-centered structural information from H-C residual dipolar couplings (RDCs) of alanine methyl groups.

A Second RNA-Binding Site in the NS1 Protein of Influenza B Virus.

Influenza viruses cause a highly contagious respiratory disease in humans. The NS1 proteins of influenza A and B viruses (NS1A and NS1B proteins, respectively) are composed of two domains, a dimeric N-terminal domain and a C-terminal domain, connected by a flexible polypeptide linker. Here we report the 2.

(19)F NMR reveals multiple conformations at the dimer interface of the nonstructural protein 1 effector domain from influenza A virus.

Nonstructural protein 1 of influenza A virus (NS1A) is a conserved virulence factor comprised of an N-terminal double-stranded RNA (dsRNA)-binding domain and a multifunctional C-terminal effector domain (ED), each of which can independently form symmetric homodimers. Here we apply (19)F NMR to NS1A from influenza A/Udorn/307/1972 virus (H3N2) labeled with 5-fluorotryptophan, and we demonstrate that the (19)F signal of Trp187 is a sensitive, direct monitor of the ED helix:helix dimer interface. (19)F relaxation dispersion data reveal the presence of conformational dynamics within this functionally important protein:protein interface, whose rate is more than three orders of magnitude faster than the kinetics of ED dimerization.

Structural and biochemical characterization of the bilin lyase CpcS from Thermosynechococcus elongatus.

Cyanobacterial phycobiliproteins have evolved to capture light energy over most of the visible spectrum due to their bilin chromophores, which are linear tetrapyrroles that have been covalently attached by enzymes called bilin lyases. We report here the crystal structure of a bilin lyase of the CpcS family from Thermosynechococcus elongatus (TeCpcS-III). TeCpcS-III is a 10-stranded β barrel with two alpha helices and belongs to the lipocalin structural family.

Solution NMR structure of the ribosomal protein RP-L35Ae from Pyrococcus furiosus.

The ribosome consists of small and large subunits each composed of dozens of proteins and RNA molecules. However, the functions of many of the individual protomers within the ribosome are still unknown. In this article, we describe the solution NMR structure of the ribosomal protein RP-L35Ae from the archaeon Pyrococcus furiosus.

Identification of influenza virus inhibitors targeting NS1A utilizing fluorescence polarization-based high-throughput assay.

This article describes the development of a simple and robust fluorescence polarization (FP)-based binding assay and adaptation to high-throughput identification of small molecules blocking dsRNA binding to NS1A protein (nonstructural protein 1 from type A influenza strains). This homogeneous assay employs fluorescein-labeled 16-mer dsRNA and full-length NS1A protein tagged with glutathione S-transferase to monitor the changes in FP and fluorescence intensity simultaneously. The assay was optimized for high-throughput screening in a 384-well format and achieved a z' score greater than 0.

Structural basis for the sequence-specific recognition of human ISG15 by the NS1 protein of influenza B virus.

Interferon-induced ISG15 conjugation plays an important antiviral role against several viruses, including influenza viruses. The NS1 protein of influenza B virus (NS1B) specifically binds only human and nonhuman primate ISG15s and inhibits their conjugation. To elucidate the structural basis for the sequence-specific recognition of human ISG15, we determined the crystal structure of the complex formed between human ISG15 and the N-terminal region of NS1B (NS1B-NTR).

Dimer interface of the effector domain of non-structural protein 1 from influenza A virus: an interface with multiple functions.

Non-structural protein 1 from influenza A virus, NS1A, is a key multifunctional virulence factor composed of two domains: an N-terminal double-stranded RNA (dsRNA)-binding domain and a C-terminal effector domain (ED). Isolated RNA-binding and effector domains of NS1A both exist as homodimers in solution. Despite recent crystal structures of isolated ED and full-length NS1A proteins from different influenza virus strains, controversy remains over the actual biologically relevant ED dimer interface.

Backbone and Ile-δ1, Leu, Val methyl 1H, 13C and 15N NMR chemical shift assignments for human interferon-stimulated gene 15 protein.

Human interferon-stimulated gene 15 protein (ISG15), also called ubiquitin cross-reactive protein (UCRP), is the first identified ubiquitin-like protein containing two ubiquitin-like domains fused in tandem. The active form of ISG15 is conjugated to target proteins via the C-terminal glycine residue through an isopeptide bond in a manner similar to ubiquitin. The biological role of ISG15 is strongly associated with the modulation of cell immune function, and there is mounting evidence suggesting that many viral pathogens evade the host innate immune response by interfering with ISG15 conjugation to both host and viral proteins in a variety of ways.

Synthesis and evaluation of quinoxaline derivatives as potential influenza NS1A protein inhibitors.

A library of quinoxaline derivatives were prepared to target non-structural protein 1 of influenza A (NS1A) as a means to develop anti-influenza drug leads. An in vitro fluorescence polarization assay demonstrated that these compounds disrupted the dsRNA-NS1A interaction to varying extents. Changes of substituent at positions 2, 3 and 6 on the quinoxaline ring led to variance in responses.

Structure of the iSH2 domain of human phosphatidylinositol 3-kinase p85β subunit reveals conformational plasticity in the interhelical turn region.

Phosphatidylinositol 3-kinase (PI3K) proteins actively trigger signaling pathways leading to cell growth, proliferation and survival. These proteins have multiple isoforms and consist of a catalytic p110 subunit and a regulatory p85 subunit. The iSH2 domain of the p85β isoform has been implicated in the binding of nonstructural protein 1 (NS1) of influenza A viruses.

The high-throughput protein sample production platform of the Northeast Structural Genomics Consortium.

We describe the core Protein Production Platform of the Northeast Structural Genomics Consortium (NESG) and outline the strategies used for producing high-quality protein samples. The platform is centered on the cloning, expression and purification of 6X-His-tagged proteins using T7-based Escherichia coli systems. The 6X-His tag allows for similar purification procedures for most targets and implementation of high-throughput (HTP) parallel methods.

Structures of influenza A proteins and insights into antiviral drug targets.

The world is currently undergoing a pandemic caused by an H1N1 influenza A virus, the so-called 'swine flu'. The H5N1 ('bird flu') influenza A viruses, now circulating in Asia, Africa and Europe, are extremely virulent in humans, although they have not so far acquired the ability to transfer efficiently from human to human. These health concerns have spurred considerable interest in understanding the molecular biology of influenza A viruses.

Improving NMR protein structure quality by Rosetta refinement: a molecular replacement study.

The structure of human protein HSPC034 has been determined by both solution nuclear magnetic resonance (NMR) spectroscopy and X-ray crystallography. Refinement of the NMR structure ensemble, using a Rosetta protocol in the absence of NMR restraints, resulted in significant improvements not only in structure quality, but also in molecular replacement (MR) performance with the raw X-ray diffraction data using MOLREP and Phaser. This method has recently been shown to be generally applicable with improved MR performance demonstrated for eight NMR structures refined using Rosetta (Qian et al.

Structural basis for suppression of a host antiviral response by influenza A virus.

Influenza A viruses are responsible for seasonal epidemics and high mortality pandemics. A major function of the viral NS1A protein, a virulence factor, is the inhibition of the production of IFN-beta mRNA and other antiviral mRNAs. The NS1A protein of the human influenza A/Udorn/72 (Ud) virus inhibits the production of these antiviral mRNAs by binding the cellular 30-kDa subunit of the cleavage and polyadenylation specificity factor (CPSF30), which is required for the 3' end processing of all cellular pre-mRNAs.

Structure of an acetyl-CoA binding protein from Staphylococcus aureus representing a novel subfamily of GCN5-related N-acetyltransferase-like proteins.

We have determined the solution NMR structure of SACOL2532, a putative GCN5-like N-acetyltransferase (GNAT) from Staphylococcus aureus. SACOL2532 was shown to bind both CoA and acetyl-CoA, and structures with and without bound CoA were determined. Based on analysis of the structure and sequence, a subfamily of small GCN5-related N-acetyltransferase (GNAT)-like proteins can be defined.

Crystal structure of AGR_C_4470p from Agrobacterium tumefaciens.

We report here the crystal structure at 2.0 A resolution of the AGR_C_4470p protein from the Gram-negative bacterium Agrobacterium tumefaciens. The protein is a tightly associated dimer, each subunit of which bears strong structural homology with the two domains of the heme utilization protein ChuS from Escherichia coli and HemS from Yersinia enterocolitica.