Prions, beta-sheets and transmissible dementias: is there still something missing?

A single residue in influenza virus H2 hemagglutinin enhances the breadth of the B cell response elicited by H2 vaccination

Conserved epitopes on the influenza hemagglutinin (HA) stem are an attractive target for universal vaccine strategies as they elicit broadly neutralizing antibodies. Such antibody responses to stem-specific epitopes have been extensively characterized for HA subtypes H1 and H5 in humans. H2N2 influenza virus circulated 50 years ago and represents a pandemic threat due to the lack of widespread immunity, but, unlike H1 and H5, the H2 HA stem contains Phe45_HA2 predicted to sterically clash with HA stem-binding antibodies characterized to date. To understand the effect of Phe45_HA2, we compared the HA stem-specific B cell response in post hoc analyses of two phase 1 clinical trials, one testing vaccination with an H2 ferritin nanoparticle immunogen ( NCT03186781 ) and one with an inactivated H5N1 vaccine ( NCT01086657 ). In H2-naive individuals, the magnitude of the B cell response was equivalent, but H2-elicited HA stem-binding B cells displayed greater cross-reactivity than those elicited by H5. However, in individuals with childhood H2 exposure, H5-elicited HA stem-binding B cells also displayed high cross-reactivity, suggesting recall of memory B cells formed 50 years ago. Overall, we propose that a one-residue difference on an HA immunogen can alter establishment and expansion of broadly neutralizing memory B cells. These data have implications for stem-based universal influenza vaccination strategies.

Cryo-EM structure of SARS-CoV-2 ORF3a in lipid nanodiscs

SARS-CoV-2 ORF3a is a putative viral ion channel implicated in autophagy inhibition, inflammasome activation and apoptosis. 3a protein and anti-3a antibodies are found in infected patient tissues and plasma. Deletion of 3a in SARS-CoV-1 reduces viral titer and morbidity in mice, suggesting it could be an effective target for vaccines or therapeutics. Here, we present structures of SARS-CoV-2 3a determined by cryo-EM to 2.1-Å resolution. 3a adopts a new fold with a polar cavity that opens to the cytosol and membrane through separate water- and lipid-filled openings. Hydrophilic grooves along outer helices could form ion-conduction paths. Using electrophysiology and fluorescent ion imaging of 3a-reconstituted liposomes, we observe Ca²⁺-permeable, nonselective cation channel activity, identify mutations that alter ion permeability and discover polycationic inhibitors of 3a activity. 3a-like proteins are found across coronavirus lineages that infect bats and humans, suggesting that 3a-targeted approaches could treat COVID-19 and other coronavirus diseases.

Proteomic patterns associated with heterosis

Heterosis is characterized by higher seed yields, plant biomass or other traits in heterozygotes or hybrids compared with their genetically divergent parents, which are often homozygous. Despite extensive investigation of heterosis and its wide application in crops such as maize, rice, wheat and sorghum, its molecular basis is still enigmatic. In the past century, some pioneers have proposed multigene models referring to the complementation of allelic and gene expression variation, which is likely to be an important contributor to heterosis. In addition, there are potential interactions of epigenetic variation involved in heterosis via novel mechanisms. At the level of gene expression, many recent studies have revealed that the heterosis phenomenon can be deciphered not only at the transcriptional level but also at the proteomic level. This review presents an update on the information supporting the involvement of proteomic patterns in heterosis and a possible future direction of the field. This article is part of a Special Issue entitled: Plant Proteomics--a bridge between fundamental processes and crop production, edited by Dr. Hans-Peter Mock.

Tubulovesicular structures: what are they really?

The tubulovesicular structures (TVS) are the only structures unique at the level of thin-section electron microscopy for all TSEs so far examined. They were first described in NIH Swiss mice infected intracerebrally with the "Chandler" strain of scrapie by David-Ferreira et al. in 1968 [Proc. Soc. Exp. Biol. Med. 127:313-320]. TVS were described as "particles and rods ranging in diameter from 320 to 360 A(o)." The exact topology of TVS is not entirely clear. In most published electron micrographs, TVS appeared as spheres measuring between 20 and 40 nm in diameter. The number of neuritic processes containing TVS increases through the incubation period and has been shown to correlate with the incubation period and titre of infectivity in three longitudinal disease studies of scrapie and CJD. These studies, therefore, suggest that TVS may represent a primary pathogenetic event rather than a pathological product of disease. The predominant theory of the scrapie agent is now the "prion hypothesis" and its derivatives, which implies that a conformationally altered abnormal isoform (PrP(Sc) or PrP*) of a normal cellular membrane glycoprotein (PrP(c)) is the agent and its accumulation merely mimicks replication. If an abnormal fraction of PrP is indeed the infectious agent, (although it is no longer suggested in some quarters that protease resistant fraction of PrP(Sc) is the agent). The absence of stainable PrP in TVS, however, would indicate that they are not the ultrastructural correlate of the agent. However, TVS appear to be specific and unique to the TSEs, appearing before the earliest pathological changes and increasing in line with incubation period or titre. The very existence of TVS and their correlation with infectivity, therefore, urgently needs an explanation.

The prionoses and other conformational disorders

The basic pathogenesis of numerous neurodegenerative disorders is now thought to be related to abnormal protein conformation. The common theme in all these diseases is the conversion of a normal cellular and/or circulating protein into an insoluble, aggregated, beta-sheet rich form which is deposited in the brain, sometimes in the form of amyloid. These deposits are toxic and produce neuronal dysfunction and death. The most common of these illnesses is Alzheimer's disease (AD), in which a central event is the conversion of the normal soluble amyloid beta (sA beta) peptide to amyloid beta (A beta) within neuritic plaques and cerebral vessels. A unique category of the conformational conditions are prion related diseases (or prionoses), where the etiology is thought to be related to conversion of the normal prion protein, PrPC, into an infectious and pathogenic form, PrPSc. In the case of AD and the prionoses, the conformational change can be influenced by the presence of mutations in various gene products, as well as by chaperone proteins. Apolipoprotein E is thought to act as such a chaperone protein in AD; however, among the prionoses such a protein has been hypothesized to exist only by indirect evidence and is called "protein X". Our growing understanding of the mechanisms involved in this category of diseases, raises the possibility of therapeutic approaches based directly on the prevention and reversal of pathologic protein conformation.

Sleep, genes and death: fatal familial insomnia

Over the past 30 years, significant progress has been made in understanding the physiologic mechanisms of sleep. Insomnia, a common complaint in general medical practice, and other sleep disorders have become increasingly recognized. In 1986, a heritable total insomnia was described and termed fatal familial insomnia; since then, the pathology of this disease has been shown to involve an accumulation of prion particles in the brains of affected patients. Prions have been more commonly associated with the transmission of spongiform encephalopathies such as scrapie (in sheep), Creutzfeldt-Jakob disease and Kuru. We briefly review the physiological and biochemical characteristics of normal sleep, describe the typical clinical characteristics of fatal familial insomnia and describe the current understanding of how prions cause neurodegenerative diseases, including fatal familial insomnia.

Formation of a native-like subdomain in a partially folded intermediate of bovine pancreatic trypsin inhibitor

In the folding of bovine pancreatic trypsin inhibitor (BPTI), the single-disulfide intermediate [30-51] plays a key role. We have investigated a recombinant analog of [30-51] using a 2-dimensional nuclear magnetic resonance (2D-NMR). This recombinant analog, named [30-51]Ala, contains a disulfide bond between Cys-30 and Cys-51, but contains alanine in place of the other cysteines in BPTI to prevent the formation of other intermediates. By 2D-NMR, [30-51]Ala consists of 2 regions-one folded and one predominantly unfolded. The folded region resembles a previously characterized peptide model of [30-51], named P alpha P beta, that contains a native-like subdomain with tertiary packing. The unfolded region includes the first 14 N-terminal residues of [30-51] and is as unfolded as an isolated peptide containing these residues. Using protein dissection, we demonstrate that the folded and unfolded regions of [30-51]Ala are structurally independent. The partially folded structure of [30-51]Ala explains many of the properties of authentic [30-51] in the folding pathway of BPTI. Moreover, direct structural characterization of [30-51]Ala has revealed that a crucial step in the folding pathway of BPTI coincides with the formation of a native-like subdomain, supporting models for protein folding that emphasize the formation of cooperatively folded subdomains.