Alzheimer's disease is the most fatal neurodegenerative disorder wherein the process of amyloid-beta (Abeta) amyloidogenesis appears causative. Here, we present the 3D structure of the fibrils comprising Abeta(1-42), which was obtained by using hydrogen-bonding constraints from quenched hydrogen/deuterium-exchange NMR, side-chain packing constraints from pairwise mutagenesis studies, and parallel, in-register beta-sheet arrangement from previous solid-state NMR studies. Although residues 1-17 are disordered, residues 18-42 form a beta-strand-turn-beta-strand motif that contains two intermolecular, parallel, in-register beta-sheets that are formed by residues 18-26 (beta1) and 31-42 (beta2). At least two molecules of Abeta(1-42) are required to achieve the repeating structure of a protofilament. Intermolecular side-chain contacts are formed between the odd-numbered residues of strand beta1 of the nth molecule and the even-numbered residues of strand beta2 of the (n - 1)th molecule. This interaction pattern leads to partially unpaired beta-strands at the fibrillar ends, which explains the sequence selectivity, the cooperativity, and the apparent unidirectionality of Abeta fibril growth. It also provides a structural basis for fibrillization inhibitors.

Prions are believed to be infectious self-propagating polymers of otherwise soluble host-encoded proteins 1,2 . This concept is now strongly supported by the recent findings that amyloid fibrils of recombinant prion proteins from yeast 3-5 , Podospora anserina 6 , and mammals 7 can induce prion phenotypes in the corresponding hosts. However, the structural basis of prion infectivity remains largely elusive because acquisition of atomic resolution structural properties of amyloid fibrils represents a largely unsolved technical challenge. HET-s, the prion protein of P. anserina, contains a C-terminal prion domain comprising residues 218-289. Amyloid fibrils of are necessary and sufficient for the induction and propagation of prion infectivity 6 . Here, we have used fluorescence studies, quenched hydrogen exchange NMR and solid state NMR to determine the sequence specific positions of secondary structure elements of amyloid fibrils of . This revealed four β-strands constituted by two pseudo repeat sequences, each forming a β-strandturn-β-strand motif. We show that this conformation is the functional and infectious entity of the HET-s prion by using a structure-based mutagenesis approach. These results correlate for the first time distinct structural elements with prion infectivity.The prion form of the protein HET-s is involved in a programmed cell death phenomenon termed heterokaryon incompatibility 8,9 . This reaction occurs in filamentous fungi when cells of incompatible genotype fuse and form a mixed cell. In P. anserina, two incompatible genotypes, called het-s and het-S, encode for the proteins HET-s and HET-S. They are both 289 amino acids long and differ in only 13 residues 10 . However, only HET-s can form a prion 11 : P. anserina cells expressing the HET-s protein exist either in a prion state called [Hets] Correspondence and requests for materials should be addressed to R.R. (e-mail: riek@salk.edu).. $ these authors contributed equally to this work.Supplementary Information accompanies the paper on Nature's website (http://www.nature.com). (Fig. 1a) contained one assigned cross-peak for each backbone amide of with the exception of 289, enabling a residuespecific determination of the hydrogen exchange rates. Upon exchange in D 2 O buffer for 6 weeks the intensity of about 45% of the resonances was significantly reduced or absent from the spectrum (Fig. 1b). This suggested that the corresponding amides have undergone exchange with solvent deuterons, which are not visible in this experiment. NIH Public AccessThe hydrogen exchange was followed over a total period of 3 months. All residues displayed a mono-exponential decay (Fig. S1) indicating that the structure of the fibrils was well defined and homogeneous. The summarized hydrogen exchange data (Fig. 1e) show that due to exchange rates faster than 5·h -1 , the 8 N-terminal residues, the 5 C-terminal residues and residues 247-261 are only weakly or not protected and may therefore be conformationally disordered. Four segments were observed that d...

Currently approved viral vector-based and mRNA-based vaccine approaches against coronavirus disease 2019 (COVID-19) consider only homologous prime-boost vaccination. After reports of thromboembolic events, several European governments recommended using AstraZeneca’s ChAdOx1-nCov-19 (ChAd) only in individuals older than 60 years, leaving millions of already ChAd-primed individuals with the decision to receive either a second shot of ChAd or a heterologous boost with mRNA-based vaccines. However, such combinations have not been tested so far. We used Hannover Medical School’s COVID-19 Contact Study cohort of healthcare professionals to monitor ChAd-primed immune responses before and 3 weeks after booster with ChAd (n = 32) or BioNTech/Pfizer’s BNT162b2 (n = 55). Although both vaccines boosted prime-induced immunity, BNT162b2 induced significantly higher frequencies of spike-specific CD4+ and CD8+ T cells and, in particular, high titers of neutralizing antibodies against the B.1.1.7, B.1.351 and P.1 variants of concern of severe acute respiratory syndrome coronavirus 2.

We report the observation of undetected (until now) residues of the prion protein fragment HET-s(218-289) which give rise to well-resolved (13)C, (15)N, and (1)H NMR resonances under high-resolution magic-angle spinning (HRMAS) conditions. The observed signals belong to large polymeric units as shown by measuring the lateral diffusion constants. The amino acids identified in the spectra are compatible with their localization in the segments of the protein which could not be detected in earlier solid-state NMR experiments. The observed chemical shifts indicate that these residues are in a random-coil conformation. Complementary experiments which detect only dynamic or static residues, respectively, strongly suggest that they belong to different parts of the same molecule.