Although the rates of chemical reactions become faster with increasing temperature, the converse may be observed with protein-folding reactions. The rate constant for folding initially increases with temperature, goes through a maximum, and then decreases. The activation enthalpy is thus highly temperature dependent because of a large change in specific heat (delta Cp). Such a delta Cp term is usually presumed to be a consequence of a large decrease in exposure of hydrophobic surfaces to water as the reaction proceeds from the denatured state to the transition state for folding: the hydrophobic side chains are surrounded by "icebergs" of water that melt with increasing temperature, thus making a large contribution to the Cp of the denatured state and a smaller one to the more compact transition state. The rate could also be affected by temperature-induced changes in the conformational population of the ground state: the heat required for the progressive melting of residual structure in the denatured state will contribute to delta Cp. By examining two proteins with different refolding mechanisms, we are able to find both of these two processes; barley chymotrypsin inhibitor 2, which refolds from a highly unfolded state, fits well to a hydrophobic interaction model with a constant delta Cp of activation, whereas barnase, which refolds from a more structured denatured state, deviates from this ideal behavior.

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A new coronavirus (severe acute respiratory syndrome coronavirus [SARS-CoV]) has been identified to be the etiological agent of severe acute respiratory syndrome. Given the highly contagious and acute nature of the disease, there is an urgent need for the development of diagnostic assays that can detect SARS-CoV infection. For determination of which of the viral proteins encoded by the SARS-CoV genome may be exploited as diagnostic antigens for serological assays, the viral proteins were expressed individually in mammalian and/or bacterial cells and tested for reactivity with sera from SARS-CoV-infected patients by Western blot analysis. A total of 81 sera, including 67 from convalescent patients and seven pairs from two time points of infection, were analyzed, and all showed immunoreactivity towards the nucleocapsid protein (N). Sera from some of the patients also showed immunoreactivity to U274 (59 of 81 [73%]), a protein that is unique to SARS-CoV. In addition, all of the convalescent-phase sera showed immunoreactivity to the spike (S) protein when analyzed by an immunofluorescence method utilizing mammalian cells stably expressing S. However, samples from the acute phase (2 to 9 days after the onset of illness) did not react with S, suggesting that antibodies to N may appear earlier than antibodies to S. Alternatively, this could be due to the difference in the sensitivities of the two methods. The immunoreactivities to these recombinant viral proteins are highly specific, as sera from 100 healthy donors did not react with any of them. These results suggest that recombinant N, S, and U274 proteins may be used as antigens for the development of serological assays for SARS-CoV.

Nitric oxide is an important molecule playing a key role in a broad range of biological process such as neurotransmission, vasodilatation and immune responses. While the anti-microbiological properties of nitric oxide-derived reactive nitrogen intermediates (RNI) such as peroxynitrite, are known, the mechanism of these effects are as yet poorly studied. Severe Acute Respiratory Syndrome coronavirus (SARS-CoV) belongs to the family Coronaviridae, was first identified during 2002-2003. Mortality in SARS patients ranges from between 6 to 55%. We have previously shown that nitric oxide inhibits the replication cycle of SARS-CoV in vitro by an unknown mechanism. In this study, we have further investigated the mechanism of the inhibition process of nitric oxide against SARS-CoV. We found that peroxynitrite, an intermediate product of nitric oxide in solution formed by the reaction of NO with superoxide, has no effect on the replication cycle of SARS-CoV, suggesting that the inhibition is either directly effected by NO or a derivative other than peroxynitrite. Most interestingly, we found that NO inhibits the replication of SARS-CoV by two distinct mechanisms. Firstly, NO or its derivatives cause a reduction in the palmitoylation of nascently expressed spike (S) protein which affects the fusion between the S protein and its cognate receptor, angiotensin converting enzyme 2. Secondly, NO or its derivatives cause a reduction in viral RNA production in the early steps of viral replication, and this could possibly be due to an effect on one or both of the cysteine proteases encoded in Orf1a of SARS-CoV.

Using AI we identified baricitinib as possessing anti-viral and anti-cytokine efficacy. We now show a 71% (95% CI 0.15-0.58) mortality benefit in 83 patients with moderate-severe SARS-CoV-2 pneumonia with few drug-induced adverse events, including a large elderly cohort (median age 81 years). A further 48 cases with mild-moderate pneumonia recovered uneventfully. Using organotypic 3D cultures of primary human liver cells, we demonstrate that interferon-alpha-2 (IFNα2) significantly increases ACE2 expression and SARS-CoV-2 infectivity in parenchymal cells by >5-fold. RNA-Seq reveals gene response signatures associated with platelet activation, fully inhibited by baricitinib. Using viral load quantifications and super-resolution microscopy, baricitinib exerts activity rapidly through the inhibition of host proteins (numb associated kinases), uniquely amongst anti-virals. This reveals mechanistic actions of a Janus kinase-1/2 inhibitor targeting viral entry, replication and the cytokine storm, and is associated with beneficial outcomes including in severely ill elderly patients, data that incentivizes further randomized controlled trials.

Previous experimental and theoretical studies have produced highresolution descriptions of the native and folding transition states of chymotrypsin inhibitor 2 (CI2). In similar fashion, here we use a combination of NMR experiments and molecular dynamics simulations to examine the conformations populated by CI2 in the denatured state. The denatured state is highly unfolded, but there is some residual native helical structure along with hydrophobic clustering in the center of the chain. The lack of persistent nonnative structure in the denatured state reduces barriers that must be overcome, leading to fast folding through a nucleation-condensation mechanism. With the characterization of the denatured state, we have now completed our description of the folding͞ unfolding pathway of CI2 at atomic resolution.CI2 ͉ nuclear magnetic resonance ͉ molecular dynamics simulations ͉ conformational transitions ͉ nucleation-condensation P rotein folding is a rapid and complex process that is difficult to characterize. To add to this difficulty, the denatured state consists of a large ensemble of conformations interconverting at a rapid rate. The denatured state is often assumed to be devoid of intramolecular interactions, such that the stability of a protein can be explained purely in terms of interactions in the native state. In recent years, it has become apparent that many proteins contain residual structure in the denatured state (ref. 1 and refs. therein). However, detailed characterization of this structure is very challenging, if not impossible in many cases. As such, during folding one follows the transition of a diverse system from an unknown starting point to a well-ordered native state. Further information about the diversity, dynamics, and structure of the denatured state is necessary to characterize and understand better this process.The simplest folding pathway to define is two state, i.e., involving only the denatured and native states, which are separated by the energetically unfavorable transition state. Chymotrypsin inhibitor 2 (CI2) was the first protein shown to fold by a two-state mechanism, and it has since been the focus of a number of experimental and theoretical studies. It is a 64-residue protein that consists of an ␣-helix and a three-stranded ␤-sheet (Fig. 1). The main hydrophobic core is formed by the packing of the ␣-helix against the ␤-sheet.Experimentally, the structure of the transition state has been studied by the protein engineering (⌽-value) method (2). In combination with molecular dynamics (MD) simulations, an atomic-resolution model of the transition state has been proposed (3-7) and verified (8). The rate-limiting step for the folding of CI2 involves the final expulsion of water molecules from the exposed nonpolar side chains and the tight packing of the hydrophobic core. The transition state is similar to an expanded native state with some disruption of the secondary structure.In contrast, the denatured state of CI2 appears to be largely unstructured as probed by NMR studies of variou...

Baricitinib is an oral Janus kinase (JAK)1/JAK2 inhibitor approved for the treatment of rheumatoid arthritis (RA) that was independently predicted, using artificial intelligence (AI) algorithms, to be useful for COVID‐19 infection via proposed anti‐cytokine effects and as an inhibitor of host cell viral propagation. We evaluated the in vitro pharmacology of baricitinib across relevant leukocyte subpopulations coupled to its in vivo pharmacokinetics and showed it inhibited signaling of cytokines implicated in COVID‐19 infection. We validated the AI‐predicted biochemical inhibitory effects of baricitinib on human numb‐associated kinase (hNAK) members measuring nanomolar affinities for AAK1, BIKE, and GAK. Inhibition of NAKs led to reduced viral infectivity with baricitinib using human primary liver spheroids. These effects occurred at exposure levels seen clinically. In a case series of patients with bilateral COVID‐19 pneumonia, baricitinib treatment was associated with clinical and radiologic recovery, a rapid decline in SARS‐CoV‐2 viral load, inflammatory markers, and IL‐6 levels. Collectively, these data support further evaluation of the anti‐cytokine and anti‐viral activity of baricitinib and support its assessment in randomized trials in hospitalized COVID‐19 patients.

In mammalian cells, IFN responses that occur during RNA and DNA virus infections are activated by distinct signaling pathways. The RIG-I-like-receptors (RLRs) bind viral RNA and engage the adaptor MAVS (mitochondrial antiviral signaling) to promote IFN expression, whereas cGAS (cGMP-AMP synthase) binds viral DNA and activates an analogous pathway via the protein STING (stimulator of IFN genes). In this study, we confirm that STING is not necessary to induce IFN expression during RNA virus infection but also find that STING is required to restrict the replication of diverse RNA viruses. The antiviral activities of STING were not linked to its ability to regulate basal expression of IFN-stimulated genes, activate transcription, or autophagy. Using vesicular stomatitis virus as a model, we identified a requirement of STING to inhibit translation during infection and upon transfection of synthetic RLR ligands. This inhibition occurs at the level of translation initiation and restricts the production of viral and host proteins. The inability to restrict translation rendered STING-deficient cells 100 times more likely to support productive viral infections than wild-type counterparts. Genetic analysis linked RNA sensing by RLRs to STING-dependent translation inhibition, independent of MAVS. Thus, STING has dual functions in host defense, regulating protein synthesis to prevent RNA virus infection and regulating IFN expression to restrict DNA viruses.