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Scientific Reports 7: Article number: 41662; published online: 06 February 2017; updated: 28 April 2017 This Article contains typographical errors. In the results section under subheading ‘The C-terminal domain adopts an immunoglobulin fold in solution’, “A search for structurally similar proteins possessing using the Dali server identified many proteins containing an Ig-like fold, including immunoglobulin receptors, fibroblast growth factor receptors and the T-cell surface glycoprotein CD4.

We report a novel method of growing silver nanostructures by cathodic sputtering onto an ionic liquid (IL) and our visualization by transmission cryo-electron microscopy to avoid beam-induced motion of the nanoparticles. By freezing the IL suspension and controlling electron dose, we can assess properties of particle size, morphology, crystallinity, and aggregation in situ and at high detail. We observed round silver nanoparticles with a well-defined diameter of 7.0 ± 1.5 nm that are faceted with crystalline cubic structures and ˜80% of the particles have multiply twinned faults. We also applied cryo-electron tomography to investigate the structure of the nanoparticles and to directly visualize the IL wetting around them. In addition to particles, we observed nanorods that appear to have assembled from individual nanoparticles. Reexamination of the samples after 4–5 days from initial preparation showed significant changes in morphology, and potential mechanisms for this are discussed.

Simple polyglutamine (polyQ) peptides aggregate in vitro via a nucleated growth pathway directly yielding amyloid-like aggregates. We show here that the 17-amino-acid flanking sequence (HTT(NT)) N-terminal to the polyQ in the toxic huntingtin exon 1 fragment imparts onto this peptide a complex alternative aggregation mechanism. In isolation, the HTT(NT) peptide is a compact coil that resists aggregation. When polyQ is fused to this sequence, it induces in HTT(NT), in a repeat-length dependent fashion, a more extended conformation that greatly enhances its aggregation into globular oligomers with HTT(NT) cores and exposed polyQ. In a second step, a new, amyloid-like aggregate is formed with a core composed of both HTT(NT) and polyQ. The results indicate unprecedented complexity in how primary sequence controls aggregation within a substantially disordered peptide and have implications for the molecular mechanism of Huntington's disease.

The crystal structure of gpD, the capsid-stabilizing protein of bacteriophage lambda, was solved at 1.1 A resolution. Data were obtained from twinned crystals in space group P21 and refined with anisotropic temperature factors to an R-factor of 0.098 (Rfree = 0. 132). GpD (109 residues) has a novel fold with an unusually low content of regular secondary structure. Noncrystallographic trimers with substantial intersubunit interfaces were observed. The C-termini are well ordered and located on one side of the trimer, relatively far from its three-fold axis. The N-termini are disordered up to Ser 15, which is close to the three-fold axis and on the same side as the C-termini. A density map of the icosahedral viral capsid at 15 A resolution, obtained by cryo-electron microscopy and image reconstruction, reveals gpD trimers, seemingly indistinguishable from the ones seen in the crystals, at all three-fold sites. The map further reveals that the side of the trimer that binds to the capsid is the side on which both termini reside. Despite this orientation of the gpD trimer, fusion proteins connected by linker peptides to either terminus bind to the capsid, allowing protein and peptide display.

Antibodies to the capsid (cAg, core antigen) of HBV play a central role in the immune response to this virus. Since most anti-cAg antibodies recognize conformational epitopes, ruling out characterization by immunochemical methods, we have approached the problem by cryo-EM and image reconstruction of Fab-decorated capsids, combined with molecular modelling. Recently, we characterized the epitopes for two anti-cAg monoclonals (mAb 88, mAb 842). Both Fabs engage sites on the protruding capsid spikes, but they differ in binding orientation and are distinct. Occupancies of symmetry-related potential binding sites are unequal, reflecting prefererential binding to certain quasiequivalent variants. Despite steric interference, it was possible to identify both epitopes. The epitope for IgG mAb 88, residues 77–87, consists of an alpha-helix on one of the polypeptide chains within the dimeric spike. That of IgM mAb 842, also conformational, consists of loops and helical regions on both polypeptide chains, residues 74–78 and 78–83 and duplicates a previously characterized epitope. To date, six epitopes have been characterized, one being linear and five conformational. Although accessible sites are limited to two small regions of the capsid surface, combinations of a small set of motifs generate substantial antigenic diversity. We estimate the total number of distinct epitopes to be about 20. from 2005 International Meeting of The Institute of Human Virology Baltimore, USA, 29 August – 2 September 2005