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Icosahedral Symmetry (icosahedral + symmetry)

Distribution by Scientific Domains

Chemistry	60%

Selected Abstracts

Cover Picture: Assembly of Wiseana Iridovirus: Viruses for Colloidal Photonic Crystals (Adv. Funct.

ADVANCED FUNCTIONAL MATERIALS, Issue 8 2006
Mater.
Abstract Assembly of colloids is a versatile tool for micro- and nanofabrication. Natural and artificially engineered viruses offer the opportunity to expand the functionality and versatility of such assemblies. The cover shows optically iridescent, thin polycrystalline arrays (background) as well as bulk pellets (inset right) that exhibit reversible hydration-dependent reflection spectra, as reported by Vaia and co-workers on p.,1086. The films and pellets were created in vitro with classical colloid-assembly techniques from Wiseana iridescent virus (inset, center) harvested from infected Wiseana spp larvae (inset, left). In,vitro assembly of Wiseana iridescent virus (WIV) yields iridescent pellets and films with structural color more vivid than in the native insect. WIV is icosahedral in shape, 140,nm in diameter, with 30,nm long fibrils attached to the outer surface, and exhibits a surface charge ca.,1/6th that of a comparable polymer colloid. The low surface charge and tethered chains on the virus surface allow the facile modification of the interparticle distance. Directed sedimentation yields predominantly an amorphous liquid-like packing of the virus. Such samples exhibit a broad reflection band that is angle independent and for which the broad maximum can be reversibly shifted from blue towards red with increased hydration. Slow sedimentation and flow-assisted assembly methods produce thin films with a polycrystalline morphology that exhibit narrower, more intense reflectivity peaks, which are hydration and angle dependent. This study points toward the potential of viral particles for photonic crystals where their unique structural features (icosahedral symmetry, extreme monodispersity, precise surface functionalization, and tethered surface chains of low surface-charge density) may lead to superior control of optical properties of their assembled arrays. [source]

Diseases caused by human papillomaviruses (HPV)

JOURNAL DER DEUTSCHEN DERMATOLOGISCHEN GESELLSCHAFT, Issue 5 2009
Alessandra Handisurya
Summary Human papillomaviruses (HPV) are non-enveloped tumor viruses with a double stranded DNA approximately 8 kilobases in length. The viral genome is enclosed by a spherical capsid with icosahedral symmetry and a diameter of about 55 nm. More than 100 HPV types have been identified. They infect the squamous epithelia of skin and mucosa and usually cause benign papillomas or warts. Persistent infection with high-risk oncogenic HPV causes all cervical cancers, most anal cancers, and a subset of vulvar, vaginal, penile and oropha-ryngeal cancers. In recent years cutaneous beta-HPV types have been associated with the pathogenesis of non-melanoma skin cancers. Two prophylactic HPV vaccines based on virus-like particles (VLP) are licensed. These are up to 100% effective in preventing HPV 16 and HPV 18 infections and associated genital lesions in women, who have not been previously infected with these types. One vaccine also prevents genital warts caused by HPV 6 and HPV 11. [source]

Cauliflower mosaic virus: still in the news

MOLECULAR PLANT PATHOLOGY, Issue 6 2002
Muriel Haas
SUMMARY Taxonomic relationship:Cauliflower mosaic virus (CaMV) is the type member of the Caulimovirus genus in the Caulimoviridae family, which comprises five other genera. CaMV replicates its DNA genome by reverse transcription of a pregenomic RNA and thus belongs to the pararetrovirus supergroup, which includes the Hepadnaviridae family infecting vertebrates. Physical properties:, Virions are non-enveloped isometric particles, 53 nm in diameter (Fig. 1). They are constituted by 420 capsid protein subunits organized following T= 7 icosahedral symmetry (Cheng, R.H., Olson, N.H. and Baker, T.S. (1992) Cauliflower mosaic virus: a 420 subunit (T= 7), multilayer structure. Virology, 16, 655,668). The genome consists of a double-stranded circular DNA of approximately 8000 bp that is embedded in the inner surface of the capsid. Figure 1. Electron micrograph of CaMV virions. Courtesy of J. Menissier de Murcia, Ecole Supérieure de Biotechnologie de Strasbourg. Viral proteins: The CaMV genome encodes six proteins, a cell-to-cell movement protein (P1), two aphid transmission factors (P2 and P3), the precursor of the capsid proteins (P4), a polyprotein precursor of proteinase, reverse transcriptase and ribonuclease H (P5) and an inclusion body protein/translation transactivator (P6). Hosts: The host range of CaMV is limited to plants of the Cruciferae family, i.e. Brassicae species and Arabidopsis thaliana, but some viral strains can also infect solanaceous plants. In nature, CaMV is transmitted by aphids in a non-circulative manner. [source]

FT-Raman characterization of the antipodal bis-adduct of C60 and anthracene

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11-12 2009
Rudolf Pfeiffer
Abstract We studied the mono- and the antipodal bis-adduct of C60 and anthracene with FT-Raman spectroscopy. Due to the reduced symmetry, the adducts have a much larger number of Raman-active modes than C60 with its icosahedral symmetry. Especially interesting is the fact that in the region of the C60 pentagonal pinch mode (PPM) the adducts show two strong peaks, of which the higher one is almost at the same frequency as the C60 mode and the lower one is downshifted by 5.4 and 10.5,cm,1 for the mono- and bis-adduct, respectively. The higher frequency peak could be explained by a degradation of the adducts into C60. However, calculated Raman spectra of the pure adducts also show two strong peaks in the PPM region, of which the higher frequency one is not PPM related. Finally, the C,H vibrations are the only clear evidence for anthracene in the adduct spectra. [source]

Discrete tomography of icosahedral model sets

ACTA CRYSTALLOGRAPHICA SECTION A, Issue 3 2009
Christian Huck
The discrete tomography of mathematical quasicrystals with icosahedral symmetry is investigated, placing emphasis on reconstruction and uniqueness problems. The work is motivated by the requirement in materials science for the unique reconstruction of the structures of icosahedral quasicrystals from a small number of images produced by quantitative high-resolution transmission electron microscopy. [source]

Towards a classification of icosahedral viruses in terms of indexed polyhedra

ACTA CRYSTALLOGRAPHICA SECTION A, Issue 5 2006
A. Janner
The standard Caspar & Klug classification of icosahedral viruses by means of triangulation numbers and the more recent novel characterization of Twarock leading to a Penrose-like tessellation of the capsid of viruses not obeying the Caspar,Klug rules can be obtained as a special case in a new approach to the morphology of icosahedral viruses. Considered are polyhedra with icosahedral symmetry and rational indices. The law of rational indices, fundamental for crystals, implies vertices at points of a lattice (here icosahedral). In the present approach, in addition to the rotations of the icosahedral group 235, crystallographic scalings play an important rôle. Crystallographic means that the scalings leave the icosahedral lattice invariant or transform it to a sublattice (or to a superlattice). The combination of the rotations with these scalings (linear, planar and radial) permits edge, face and vertex decoration of the polyhedra. In the last case, satellite polyhedra are attached to the vertices of a central polyhedron, the whole being generated by the icosahedral group from a finite set of points with integer indices. Three viruses with a polyhedral enclosing form given by an icosahedron, a dodecahedron and a triacontahedron, respectively, are presented as illustration. Their cores share the same polyhedron as the capsid, both being in a crystallographic scaling relation. [source]

Structural study and thermodynamic characterization of inhibitor binding to lumazine synthase from Bacillus anthracis

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 9 2010
Ekaterina Morgunova
The crystal structure of lumazine synthase from Bacillus anthracis was solved by molecular replacement and refined to Rcryst = 23.7% (Rfree = 28.4%) at a resolution of 3.5,Å. The structure reveals the icosahedral symmetry of the enzyme and specific features of the active site that are unique in comparison with previously determined orthologues. The application of isothermal titration calorimetry in combination with enzyme kinetics showed that three designed pyrimidine derivatives bind to lumazine synthase with micromolar dissociation constants and competitively inhibit the catalytic reaction. Structure-based modelling suggested the binding modes of the inhibitors in the active site and allowed an estimation of the possible contacts formed upon binding. The results provide a structural framework for the design of antibiotics active against B. anthracis. [source]

From structure of the complex to understanding of the biology

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 1 2007
Michael G. Rossmann
The most extensive structural information on viruses relates to apparently icosahedral virions and is based on X-ray crystallography and on cryo-electron microscopy (cryo-EM) single-particle reconstructions. Both techniques lean heavily on imposing icosahedral symmetry, thereby obscuring any deviation from the assumed symmetry. However, tailed bacteriophages have icosahedral or prolate icosahedral heads that have one obvious unique vertex where the genome can enter for DNA packaging and exit when infecting a host cell. The presence of the tail allows cryo-EM reconstructions in which the special vertex is used to orient the head in a unique manner. Some very large dsDNA icosahedral viruses also develop special vertices thought to be required for infecting host cells. Similarly, preliminary cryo-EM data for the small ssDNA canine parvovirus complexed with receptor suggests that these viruses, previously considered to be accurately icosahedral, might have some asymmetric properties that generate one preferred receptor-binding site on the viral surface. Comparisons are made between rhinoviruses that bind receptor molecules uniformly to all 60 equivalent binding sites, canine parvovirus, which appears to have a preferred receptor-binding site, and bacteriophage T4, which gains major biological advantages on account of its unique vertex and tail organelle. [source]

An icosahedral assembly of the light-harvesting chlorophyll a/b protein complex from pea chloroplast thylakoid membranes

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 5 2004
Tomoya Hino
When the light-harvesting chlorophyll a/b protein complex (LHC-II) from pea thylakoid membranes is co-crystallized with native lipids, an octahedral crystal that exhibits no birefringence is obtained. Cryogenic electron micrographs of a crystal edge showed the crystal to be made up of hollow spherical assemblies with a diameter of 250,Å. X-ray diffraction data at 9.5,Å resolution revealed the spherical shell of LHC-II to have icosahedral symmetry. A T = 1 icosahedral model of LHC-II, in which the stromal surface of the protein faces outward, was constructed using the previously reported structure of the LHC-II trimer [Kühlbrandt et al. (1994), Nature (London), 367, 614,621]. The present result shows the first example of a well ordered three-dimensional crystal of icosahedral proteoliposomes. [source]

Entrapped Bonded Hydrogen in a Fullerene: the Five-Atom Cluster Sc3CH in C80

CHEMPHYSCHEM, Issue 4 2007
Matthias Krause Dr.
Abstract The synthesis and characterisation of the new endohedral cluster fullerene Sc3CH@C80 is reported. The encapsulation of the first hydrocarbon cluster inside a fullerene was achieved by the arc burning method in a reactive CH4 atmosphere. The extensive characterisation by mass spectrometry (MS), high- pressure liquid chromatography (HPLC), 45Sc NMR, electron spin resonance (ESR), UV/Vis-NIR and Raman spectroscopy provided the experimental evidence for the caging of the five-atom Sc3CH cluster inside the C80 cage isomer with icosahedral symmetry. The proposed new structure was confirmed by DFT calculations, which gave a closed shell and large energy gap structure. Thus a pyramidal Sc3CH cluster and the Ih -C80 cage were shown to be the most stable configuration for Sc3CH@C80 whereas alternative structures give a smaller bonding energy as well as a smaller energy gap. [source]