he SARS-CoV-2 virus is thought, based on sequence identity, to have crossed from bats to humans in 2019 1 . Similar to SARS-CoV-1 (2002-2003 and MERS-CoV (2012), SARS-CoV-2 presents as a respiratory disease but can progress into internal organs and cause organ failure 2,3 . A recent report from France estimates a fatality rate of 0.7% and a hospitalization rate of 3.6% 4 . Both these rates are much higher in elderly populations 4,5 . Around 33% of those admitted to UK hospitals with COVID-19 have died 6 . Because SARS-CoV-2 also spreads rapidly in the naive human population 7 , the current COVID-19 pandemic has presented an unprecedented challenge to modern human society. Although there is currently no 'cure' or vaccine for the disease, passive immune therapy by transfusing critically ill COVID-19 patients with serum from COVID-19 convalescent individuals has been shown to improve clinical outcomes 8,9 . This would suggest that neutralization of the virus, even at a relatively late stage in the disease, may be a useful COVID-19 therapy.The single-positive-strand RNA genome of SARS-CoV-2, like SARS-CoV, encodes four major structural proteins: spike, envelope, membrane and nucleocapsid. The spike protein comprises an N-terminal (S1) subunit, which contains the roughly 200-residue receptor binding domain (RBD) 10,11 , and a C-terminal subunit (S2), which contains the fusion protein 12 (Fig. 1a). The RBD of SARS-CoV-2 binds more tightly to the extracellular domain of angiotensin-converting enzyme 2 (ACE2) (Fig. 1a) than the homologous SARS-CoV-1 RBD 13 . The higher affinity results from sequence changes in RBD (Fig. 1b) and this has been proposed to underlie the higher transmissibility of SARS-CoV-2 14 . Antibodies raised to the spike protein of SARS-CoV-1 can neutralize the virus both in vitro and in vivo, by binding to the RBD and blocking binding to ACE2 15 . Unfortunately, most of these antibodies do not cross-react with the SARS-CoV-2 RBD 13 . The CR3022 antibody derived from a convalescent SARS-CoV-1 patient is cross-reactive to both SARS-CoV-1 and SARS-CoV-2 RBD (reported apparent K D of 6 nM, ref. 16 ). Two studies have reported crystal structures of CR3022 bound to SARS-CoV-2 RBD and show that the target epitope is distant from the ACE2 binding region 17,18 , which is consistent with the observation that CR3022 does not block RBD binding to ACE2. Another study on CR3022 has reported highly effective SARS-CoV-2 neutralizing activity that appears to arise from destabilization of the spike trimer, a novel mechanism for neutralizing SARS-CoV-2 18 . Destabilization of viral proteins by antibodies has been observed for influenza 19 and human immunodeficiency virus 20 .Mammalian, including human, antibodies generally have two chains (heavy and light), but camelids, in addition to two-chain antibodies, also possess a single-heavy-chain antibody variant 21 .

Inflammatory bowel diseases (IBD), including Crohn’s disease (CD) and ulcerative colitis (UC), are complex chronic inflammatory conditions of the gastrointestinal tract that are driven by perturbed cytokine pathways. Anti-tumor necrosis factor-α (TNF) antibodies are a mainstay therapeutic approach for IBD. However, up to 40% of patients are non-responsive to anti-TNF agents, and identifying alternative therapeutic targets is a priority. Here we show that expression of the cytokine Oncostatin M (OSM) and its receptor (OSMR) is increased in the inflamed intestine of IBD patients compared to healthy controls, and correlates closely with histopathological disease severity. OSMR is expressed in non-hematopoietic, non-epithelial intestinal stromal cells, which respond to OSM by producing various pro-inflammatory molecules including interleukin-6 (IL-6), the leukocyte adhesion factor ICAM-1, and chemokines that attract neutrophils, monocytes, and T cells. In an animal model of anti-TNF resistant intestinal inflammation, genetic deletion or pharmacological blockade of OSM significantly attenuates colitis. Furthermore, high pre-treatment OSM expression is strongly associated with failure of anti-TNF therapy based on analysis of over 200 IBD patients, including two cohorts from phase 3 clinical trials of infliximab and golimumab. OSM is thus a potential biomarker and therapeutic target for IBD, with particular relevance for anti-TNF resistant patients.

This article describes the construction of a set of versatile expression vectors based on the In-Fusion™ cloning enzyme and their use for high-throughput cloning and expression screening. Modifications to commonly used vectors rendering them compatible with In-Fusion™ has produced a ligation-independent cloning system that is (1) insert sequence independent (2) capable of cloning large PCR fragments (3) efficient over a wide (20-fold) insert concentration range and (4) applicable to expression in multiple hosts. The system enables the precise engineering of (His6-) tagged constructs with no undesirable vector or restriction-site-derived amino acids added to the expressed protein. The use of a multiple host-enabled vector allows rapid screening in both E. coli and eukaryotic hosts (HEK293T cells and insect cell hosts, e.g. Sf9 cells). These high-throughput screening activities have prompted the development and validation of automated protocols for transfection of mammalian cells and Ni-NTA protein purification.

ARS-CoV-2 was first detected in December 2019, leading to a pandemic with an estimated 5-6% mortality rate 1. Akin to SARS-CoV-1, the causative agent of the 2003 SARS outbreak, this is an enveloped betacoronavirus with protrusions of large trimeric 'spike' proteins. Receptor binding domains (RBDs) located at the tips of these spikes facilitate host cell entry via interaction with angiotensin-converting enzyme 2 (ACE2) 2. Spikes are type I transmembrane glycoproteins, formed from a single polypeptide, which transitions into a post-fusion state via cleavage into S1 (N-terminal) and S2 (C-terminal) chains following receptor binding or trypsin treatment 3. In the pre-fusion state, the apical RBD (~22 kDa) is folded down, enshrouded by the N-terminal domain (NTD) of the spike so that the receptor binding site is inaccessible until, it is assumed, an RBD stochastically swings upwards to present the ACE2 binding site 4-7. ACE2 interaction locks the RBD in the 'up' conformation, which drives conversion to the post-fusion form where the S2 subunit engages the host membrane while dispensing with S1 4,5. Neutralizing human monoclonal antibodies (mAbs) that recognize the ACE2 receptor binding site for SARS-CoV-1 and SARS-CoV-2 are generally not cross-reactive between the two viruses and are susceptible to escape mutation 8-12. Indeed, a natural mutation (Y495N) has already been identified at this site (GISAID 13 : accession ID: EPI_ISL_429783 Wienecke-Baldacchino et al.). By contrast, the CR3022 antibody (derived from a SARS-CoV-1-infected patient) cross-reacts strongly with SARS-CoV-2 (see Methods and Fig. 1) and has been shown to recognize a cryptic, conserved footprint on the RBD distinct from the binding epitope of

In selecting a method to produce a recombinant protein, a researcher is faced with a bewildering array of choices as to where to start. To facilitate decision-making, we describe a consensus 'what to try first' strategy based on our collective analysis of the expression and purification of over 10,000 different proteins. This review presents methods that could be applied at the outset of any project, a prioritized list of alternate strategies and a list of pitfalls that trip many new investigators.

SummaryGlycoproteins present special problems for structural genomic analysis because they often require glycosylation in order to fold correctly, whereas their chemical and conformational heterogeneity generally inhibits crystallization. We show that the “glycosylation problem” can be solved by expressing glycoproteins transiently in mammalian cells in the presence of the N-glycosylation processing inhibitors, kifunensine or swainsonine. This allows the correct folding of the glycoproteins, but leaves them sensitive to enzymes, such as endoglycosidase H, that reduce the N-glycans to single residues, enhancing crystallization. Since the scalability of transient mammalian expression is now comparable to that of bacterial systems, this approach should relieve one of the major bottlenecks in structural genomic analysis.

Flaviviridae are small enveloped viruses hosting a positive-sense single-stranded RNA genome. Besides yellow fever virus, a landmark case in the history of virology, members of the Flavivirus genus, such as West Nile virus and dengue virus, are increasingly gaining attention due to their re-emergence and incidence in different areas of the world. Additional environmental and demographic considerations suggest that novel or known flaviviruses will continue to emerge in the future. Nevertheless, up to few years ago flaviviruses were considered low interest candidates for drug design. At the start of the European Union VIZIER Project, in 2004, just two crystal structures of protein domains from the flaviviral replication machinery were known. Such pioneering studies, however, indicated the flaviviral replication complex as a promising target for the development of antiviral compounds. Here we review structural and functional aspects emerging from the characterization of two main components (NS3 and NS5 proteins) of the flavivirus replication complex. Most of the reviewed results were achieved within the European Union VIZIER Project, and cover topics that span from viral genomics to structural biology and inhibition mechanisms. The ultimate aim of the reported approaches is to shed light on the design and development of antiviral drug leads.

Crystallization remains a critical step in X-ray structure determination. Because it is not generally possible to rationally predict crystallization conditions, commercial screens have been developed which sample a wide range of crystallization space. While this approach has proved successful in many cases, a significant number of proteins fail to crystallize despite being soluble and monodispersed. It is established that chemical modification can facilitate the crystallization of otherwise intractable proteins. Here we describe a method for the reductive methylation of lysine residues which is simple, inexpensive, and efficient, and report on its application to ten proteins. We describe the effect of methylation on the physico-chemical properties of these proteins, and show that it led to diffraction-quality crystals from four proteins and structures for three that had hitherto proved refractory to crystallization. The method is suited to both low- and high-throughput laboratories.