Viral infections have catastrophic impacts on the public. Though there have been notable advancements in detection methods, there remains need for rapid point-ofcare detection strategies for viral infections that are accurate, require minimal instrumentation, and distinguish active from resolved infection. We present a colorimetric approach for virus sensing by direct color generation on a cotton swab. By appending a chromophore to the peptide recognition sequence for SARS-CoV-2 main protease, we created a reporter that produces a color change upon protease hydrolysis. The reporter is selective towards the SARS-CoV-2 Mpro, is readily observable by eye or smartphone.
Flaviviruses, continue to threaten public health. The associated NS2B-NS3pro proteases are essential to the flaviviral life cycles and can interfere with host responses, making the proteases good drug targets. While the proteases are highly identical, the catalytic efficiency and the substrate selection are divergent, so the unique properties of viral proteases may contribute the disparate viral pathologies. NS2B-NS3 proteases transition between two widely different conformational states: an ‘open’ (inactive) conformation and a ‘closed’ (active) conformation. We developed versions of NS2B-NS3pro that allow us to trap the enzyme in distinct conformations. Enzymatic activity is dependent on the movement of NS2B and the flexibility of the protease core. Using unbiased N-terminomics to identify 31 human proteins cleaved by the NS2B-NS3 protease we observed that the NS2B is essential for recognition of host cell substrates. Replacing the NS2B region suggests that the co-factor is the principal determinant in ZVP substrate selection. Based on this observation, we report a 440 nM inhibitor of ZVP that functions by blocking interactions between the NS3 core and NS2B cofactor.