Structural conservation of the myoviridae phage tail sheath protein fold

Bacteriophage phiKZ is a giant phage that infects Pseudomonas aeruginosa, a human pathogen. The phiKZ virion consists of a 1450?? diameter icosahedral head and a 2000??-long contractile tail. The structure of the whole virus was previously reported, showing that its tail organization in the extended state is similar to the well-studied Myovirus bacteriophage T4 tail. The crystal structure of a tail sheath protein fragment of phiKZ was determined to 2.4?? resolution. Furthermore, crystal structures of two prophage tail sheath proteins were determined to 1.9 and 3.3?? resolution. Despite low sequence identity between these proteins, all of these structures have a similar fold. The crystal structure of the phiKZ tail sheath protein has been fitted into cryo-electron-microscopy reconstructions of the extended tail sheath and of a polysheath. The structural rearrangement of the phiKZ tail sheath contraction was found to be similar to that of phage T4.     

Dual binding specificity of a Borrelia hermsii-associated complement regulator-acquiring surface protein for factor H and plasminogen discloses a putative virulence factor of relapsing fever spirochetes

Tick-borne relapsing fever in North America is primarily caused by the spirochete Borrelia hermsii. The pathogen employs multiple strategies, including the acquisition of complement regulators and antigenic variation, to escape innate and humoral immunity. In this study we identified in B. hermsii a novel member of the complement regulator-acquiring surface protein (CRASP) family, designated BhCRASP-1, that binds the complement regulators factor H (FH) and FH-related protein 1 (FHR-1) but not FH-like protein 1 (FHL-1). BhCRASP-1 specifically interacts with the short consensus repeat 20 of FH, thereby maintaining FH-associated cofactor activity for factor I-mediated C3b inactivation. Furthermore, ectopic expression of BhCRASP- 1 converted the serum-sensitive Borrelia burgdorferi B313 strain into an intermediate complement-resistant strain. Finally, we report for the first time that BhCRASP-1 binds plasminogen/plasmin in addition to FH via, however, distinct nonoverlapping domains. The fact that surface-bound plasmin retains its proteolytic activity suggest that the dual binding specificity of BhCRASP-1 for FH and plasminogen/plasmin contributes to both the dissemination/invasion of B. hermsii and its resistance to innate immunity.     

Interpretation of electron density with stereographic roadmap projections

The program RIVEM (Radial Interpretation of Viral Electron density Maps) was developed to project density radially onto a sphere that is then presented as a stereographic diagram. This permits features resulting from an asymmetric reconstruction to be projected and positioned onto an icosahedral virus surface. The features that constitute the viral surface can also be simultaneously represented in terms of atoms, amino acid residues, potential charge distribution, and surface topology. The procedure can also be adapted for the investigation of various molecular interactions.     

Insight into DNA and protein transport in double-stranded DNA viruses: the structure of bacteriophage N4

Bacteriophage N4 encapsidates a 3500-aa-long DNA-dependent RNA polymerase (vRNAP), which is injected into the host along with the N4 genome upon infection. The three-dimensional structures of wild-type and mutant N4 viruses lacking gp17, gp50, or gp65 were determined by cryoelectron microscopy. The virion has an icosahedral capsid with T = 9 quasi-symmetry that encapsidates well-organized double-stranded DNA and vRNAP. The tail, attached at a unique pentameric vertex of the head, consists of a neck, 12 appendages, and six ribbons that constitute a non-contractile sheath around a central tail tube. Comparison of wild-type and mutant virus structures in conjunction with bioinformatics established the identity and virion locations of the major capsid protein (gp56), a decorating protein (gp17), the vRNAP (gp50), the tail sheath (gp65), the appendages (gp66), and the portal protein (gp59). The N4 virion organization provides insight into its assembly and suggests a mechanism for genome and vRNAP transport strategies utilized by this unique system.     

Crystal structures of human saposins C andD: implications for lipid recognition and membrane interactions

Human saposins are essential proteins required for degradation of sphingolipids and lipid antigen presentation. Despite the conserved structural organization of saposins, their distinct modes of interaction with biological membranes are not fully understood. We describe two crystal structures of human saposin C in an "open" configuration with unusual domain swapped homodimers. This form of SapC dimer supports the "clip-on" model for SapC-induced vesicle fusion. In addition, we present the crystal structure of SapD in two crystal forms. They reveal the monomer-monomer interface for the SapD dimer, which was confirmed in solution by analytical ultracentrifugation. The crystal structure of SapD suggests that side chains of Lys10 and Arg17 are involved in initial association with the preferred anionic biological membranes by forming salt bridges with sulfate or phosphate lipid headgroups.     

Preliminary X-ray crystallographic analysis of intercellular adhesion molecule-1.

Crystals of the two amino-terminal domains of intercellular adhesion molecule-1, the receptor for the major group of human rhinovirus serotypes, diffract to 3.0 A resolution. The crystals are trigonal in space group P3(1)21 or P3(2)21 with cell dimensions of a = b = 55.7 A, c = 166.3 A, with probably six molecules per unit cell.     

Pseudotype Formation of Moloney Murine Leukemia Virus with Sendai Virus Glycoprotein F

Mixed infection of cells with both Moloney murine leukemia virus (MoMLV) and related or heterologous viruses produces progeny pseudotype virions bearing the MoMLV genome encapsulated by the envelope of the other virus. In this study, pseudotype formation between MoMLV and the prototype parainfluenza virus Sendai virus (SV) was investigated. We report for the first time that SV infection of MoMLV producer cells results in the formation of MoMLV(SV) pseudotypes, which display a largely extended host range compared to that of MoMLV particles. This could be associated with SV hemagglutinin-neuraminidase (SV-HN) glycoprotein incorporation into MoMLV envelopes. In contrast, solitary incorporation of the other SV glycoprotein, SV fusion protein (SV-F), resulted in a distinct and narrow extension of the MoMLV host range to asialoglycoprotein receptor (ASGP-R)-positive cells (e.g., cultured human hepatoma cells). Since stably ASGP-R cDNA-transfected MDCK cells, but not parental ASGP-R-negative MDCK cells, were found to be transduced by MoMLV(SV-F) pseudotypes and transduction of ASGP-R-expressing cells was found to be inhibited by ASGP-R antiserum, a direct proof for the ASGP-R-restricted tropism of MoMLV(SV-F) pseudotypes was provided. Cultivation of ASGP-R-positive HepG2 hepatoma cells on Transwell-COL membranes led to a significant enhancement of MoMLV(SV-F) titers in subsequent flowthrough transduction experiments, thereby suggesting the importance of ASGP-R accessibility at the basolateral domain for MoMLV(SV-F) pseudotype transduction. The availability of such ASGP-R-restricted MoMLV(SV-F)-pseudotyped vectors opens up new perspectives for future liver-restricted therapeutic gene transfer applications.