Structural and functional impact by SARS-CoV-2 Omicron spike mutations

The Omicron variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), bearing an unusually high number of mutations, has become a dominant strain in many countries within several weeks. We report here structural, functional and antigenic properties of its full-length spike (S) protein with a native sequence in comparison with those of previously prevalent variants. Omicron S requires a substantially higher level of host receptor ACE2 for efficient membrane fusion than other variants, possibly explaining its unexpected cellular tropism. Mutations not only remodel the antigenic structure of the N-terminal domain of the S protein, but also alter the surface of the receptor-binding domain in a way not seen in other variants, consistent with its remarkable resistance to neutralizing antibodies. These results suggest that Omicron S has acquired an extraordinary ability to evade host immunity by excessive mutations, which also compromise its fusogenic capability.

Site-Specific Synthesis of N4-Acetylcytidine in RNA Reveals Physiological Duplex Stabilization

N4-acetylcytidine (ac4C) is a post-transcriptional modification of RNA that is conserved across all domains of life. All characterized sites of ac4C in eukaryotic RNA occur in the central nucleotide of a CCG consensus sequence. However, the thermodynamic consequences of cytidine acetylation in this context have never been assessed due to its challenging synthesis. Here we report the synthesis and biophysical characterization of ac4C in its endogenous eukaryotic sequence context. First, we develop a synthetic route to homogenous RNAs containing electrophilic acetyl groups. Next, we use thermal denaturation to interrogate the effects of ac4C on duplex stability and mismatch discrimination in a native sequence found in human ribosomal RNA. Finally, we demonstrate the ability of this chemistry to incorporate ac4C into the complex modification landscape of human tRNA, and use duplex melting combined with sequence analysis to highlight a potentially unique enforcing role for ac4C in this setting. By enabling the analysis of nucleic acid acetylation in its physiological sequence context, these studies establish a chemical foundation for understanding the function of a universally-conserved nucleobase in biology and disease.

Effects of sequence motifs in the yeast 3′ untranslated region determined from massively parallel assays of random sequences

Background The 3′ untranslated region (UTR) plays critical roles in determining the level of gene expression through effects on activities such as mRNA stability and translation. Functional elements within this region have largely been identified through analyses of native genes, which contain multiple co-evolved sequence features. Results To explore the effects of 3′ UTR sequence elements outside of native sequence contexts, we analyze hundreds of thousands of random 50-mers inserted into the 3′ UTR of a reporter gene in the yeast Saccharomyces cerevisiae. We determine relative protein expression levels from the fitness of transformants in a growth selection. We find that the consensus 3′ UTR efficiency element significantly boosts expression, independent of sequence context; on the other hand, the consensus positioning element has only a small effect on expression. Some sequence motifs that are binding sites for Puf proteins substantially increase expression in the library, despite these proteins generally being associated with post-transcriptional downregulation of native mRNAs. Our measurements also allow a systematic examination of the effects of point mutations within efficiency element motifs across diverse sequence backgrounds. These mutational scans reveal the relative in vivo importance of individual bases in the efficiency element, which likely reflects their roles in binding the Hrp1 protein involved in cleavage and polyadenylation. Conclusions The regulatory effects of some 3′ UTR sequence features, like the efficiency element, are consistent regardless of sequence context. In contrast, the consequences of other 3′ UTR features appear to be strongly dependent on their evolved context within native genes.

Guaranteed Diversity and Optimality in Cost Function Network Based Computational Protein Design Methods

Proteins are the main active molecules of life. Although natural proteins play many roles, as enzymes or antibodies for example, there is a need to go beyond the repertoire of natural proteins to produce engineered proteins that precisely meet application requirements, in terms of function, stability, activity or other protein capacities. Computational Protein Design aims at designing new proteins from first principles, using full-atom molecular models. However, the size and complexity of proteins require approximations to make them amenable to energetic optimization queries. These approximations make the design process less reliable, and a provable optimal solution may fail. In practice, expensive libraries of solutions are therefore generated and tested. In this paper, we explore the idea of generating libraries of provably diverse low-energy solutions by extending cost function network algorithms with dedicated automaton-based diversity constraints on a large set of realistic full protein redesign problems. We observe that it is possible to generate provably diverse libraries in reasonable time and that the produced libraries do enhance the Native Sequence Recovery, a traditional measure of design methods reliability.

Guaranted Diversity and Optimality in Cost Function Network Based Computational Protein Design Methods

Proteins are the main active molecules of Life. While natural proteins play many roles, as enzymes or antibodies for example, there is a need to go beyond the repertoire of natural proteins to produce engineered proteins that precisely meet application requirements, in terms of function, stability, activity or other protein capacities. Computational Protein Design aims at designing new proteins from first principles, using full-atom molecular models. However, the size and complexity of proteins require approximations to make them amenable to energetic optimization queries. These approximations make the design process less reliable and a provable optimal solution may fail. In practice, expensive libraries of solutions are therefore generated and tested. In this paper, we explore the idea of generating libraries of provably diverse low energy solutions by extending Cost Function Network algorithms with dedicated automaton-based diversity constraints on a large set of realistic full protein redesign problems. We observe that it is possible to generate provably diverse libraries in reasonable time and that the produced libraries do enhance the Native Sequence Recovery, a traditional measure of design methods reliability.

High-Potency Polypeptide-based Interference for Coronavirus Spike Glycoproteins

The world is experiencing an unprecedented coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). SARS-CoV-2 spike protein-based vaccines are currently the main preventive agent to fight against the virus. However, several variants with extensive mutations in SARS-CoV-2 spike proteins have emerged. Some of these variants exhibited increased replication, higher transmission and virulence, and were partially resistant to antibody neutralization from natural infection or vaccination. With over 130 million confirmed cases and widespread vaccination around the globe, the emergence of new escape SARS-CoV-2 variants could be accelerated. New therapeutics insensitive to mutations are thus urgently needed. Here we have developed an inhibitor based on SARS-CoV-2 spike protein that potently reduced pseudovirus infectivity by limiting the level of SARS-CoV-2 spike proteins on virion envelope. Most importantly, the inhibitor was equally effective against other coronavirus spike proteins that shared as low as 35% amino-acid sequence identity, underscoring its extreme tolerance to mutations. The small-sized inhibitor would also allow simple delivery by, for instance, nasal spray. We expect the inhibitor reported here to be an invaluable aid to help end COVID-19 pandemic. Furthermore, the use of a partial native sequence or its homologues to interfere with the functions of the native protein represents a novel concept for targeting other viral proteins in combating against important viral pathogens.

High-Potency Polypeptide-based Interference for Coronavirus Spike Glycoproteins

The world is experiencing an unprecedented coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). SARS-CoV-2 spike protein-based vaccines are currently the main preventive agent to fight against the virus. However, several variants with extensive mutations in SARS-CoV-2 spike proteins have emerged. Some of these variants exhibited increased replication, higher transmission and virulence, and were partially resistant to antibody neutralization from natural infection or vaccination. With over 130 million confirmed cases and widespread vaccination around the globe, the emergence of new escape SARS-CoV-2 variants could be accelerated. New therapeutics insensitive to mutations are thus urgently needed. Here we have developed an inhibitor based on SARS-CoV-2 spike protein that potently reduced pseudovirus infectivity by limiting the level of SARS-CoV-2 spike proteins on virion envelope. Most importantly, the inhibitor was equally effective against other coronavirus spike proteins that shared as low as 35% amino-acid sequence identity, underscoring its extreme tolerance to mutations. The small-sized inhibitor would also allow simple delivery by, for instance, nasal spray. We expect the inhibitor reported here to be an invaluable aid to help end COVID-19 pandemic. Furthermore, the use of a partial native sequence or its homologues to interfere with the functions of the native protein represents a novel concept for targeting other viral proteins in combating against important viral pathogens.

Modeling Substrate Coordination to Zn-Bound Angiotensin Converting Enzyme 2

The spike protein in the envelope of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) interacts with the receptor Angiotensin Converting Enzyme 2 (ACE2) on the host cell to facilitate the viral uptake. Angiotensin II (Ang II) peptide, which has a naturally high affinity for ACE2, may be useful in inhibiting this interaction. In this study, we computationally designed several Ang II mutants to find a strong binding sequence to ACE2 receptor and examined the role of ligand substitution in the docking of native as well as mutant Ang II to the ACE2 receptor. The peptide in the ACE2-peptide complex was coordinated to zinc in the ACE2 cleft. Exploratory molecular dynamics (MD) simulations were used to measure the time-based stability of the native and mutant peptides and their receptor complexes. The MD-generated root-mean-square deviation (RMSD) values are mostly similar between the native and seven mutant peptides considered in this work, although the values for free peptides demonstrated higher variation, and often were higher in amplitude than peptides associated with the ACE2 complex. An observed lack of a strong secondary structure in the short peptides is attributed to the latter's greater flexibility and movement. The strongest binding energies within the ACE2-peptide complexes were observed in the native Ang II and only one of its mutant variants, suggesting ACE2 cleft is designed to provide optimal binding to the native sequence. An examination of the S1 binding site on ACE2 suggests that complex formation alone with these peptides may not be sufficient to allosterically inhibit the binding of SARS-CoV-2 spike proteins. However, it opens up the potential for utilizing AngII-ACE2 binding in the future design of molecular and supramolecular structures to prevent spike protein interaction with the receptor through creation of steric hindrance.

αB-crystallin affects the morphology of Aβ(1-40) aggregates

SummaryαB-crystallin (ABC) is a human small heat shock protein that is strongly linked to Alzheimer’s disease (AD). In vitro, it can inhibit the aggregation and amyloid formation of a range of proteins including Aβ(1-40), a primary component of AD amyloid plaques. Despite the strong links, the mechanism by which ABC inhibits amyloid formation has remained elusive, in part due to the notorious irreproducibility of aggregation assays involving preparations of Aβ-peptides of native sequence. Here, we present a recombinant expression protocol to produce native Aβ(1-40), devoid of any modifications or exogenous residues, with yields up to 4 mg/L E. coli. This material provides highly reproducible aggregation kinetics and, by varying the solution conditions, we obtain either highly ordered amyloid fibrils or more disordered aggregates. Addition of ABC slows the aggregation of Aβ(1-40), and interferes specifically with the formation of ordered amyloid fibrils, favouring instead the more disordered aggregates. Solution-state NMR spectroscopy reveals that the interaction of ABC with Aβ(1-40) depends on the specific aggregate morphology. These results provide mechanistic insight into how ABC inhibits the formation of amyloid fibrils.HighlightsProtocol for production of native recombinant Aβ(1-40)Amyloid formation under physiological conditions is highly reproducibleBoth ordered fibrils and disordered aggregates can be reliably formedαB-crystallin specifically inhibits amyloid fibril assembling, favouring disordered aggregateseTOC blurbMüller et al. introduce a protocol for the highly reproducible production of amyloid from native Aβ(1-40) and determine that the human chaperone ABC specifically destabilises them in favour of disordered aggregates. NMR shows that ABC can distinguish between aggregate morphologies.Graphical Abstract

Characterization and Validation of Arg286 Residue of IL-1RAcP as a Potential Drug Target for Osteoarthritis

Osteoarthritis (OA) is the most common form of arthritis and the fastest growing cause of chronic disability in the world. Formation of the ternary IL-1β /IL-1R1/IL-1RAcP protein complex and its downstream signaling has been implicated in osteoarthritis pathology. Current OA therapeutic approaches target either the cytokine IL-1β or the primary receptor IL-1RI but do not exploit the potential of the secondary receptor IL-1RAcP. Our previous work implicated the Arg286 residue of IL-1RAcP as a key mediator of complex formation. Molecular modeling confirmed Arg286 as a high-energy mediator of the ternary IL-1β complex architecture and interaction network. Anti-IL-1RAcP monoclonal antibodies (mAb) targeting the Arg286 residue were created and were shown to effectively reduce the influx of inflammatory cells to damaged joints in a mouse model of osteoarthritis. Inhibitory peptides based on the native sequence of IL-1RAcP were prepared and examined for efficacy at disrupting the complex formation. The most potent peptide inhibitor had an IC50 value of 304 pM in a pull-down model of complex formation, and reduced IL-1β signaling in a cell model by 90% at 2 μM. Overall, therapies that target the Arg286 region surface of IL-1RAcP, and disrupt subsequent interactions with subunits, have the potential to serve as next generation treatments for osteoarthritis.