Bands near the 25 kDa MW marker were observed in the samples treated with the SARS-CoV-2 PLpro and MERS PLpro. be related to the virus-induced phenotype associated with Group IV viruses, suggesting that information about viral pathogenesis may be extractable directly from the viral genome sequence. Here we identify sequences cleaved by the SARS-CoV-2 papain-like protease (PLpro) within human MYH7 and MYH6 (two cardiac myosins linked to several cardiomyopathies), FOXP3 (an X-linked Treg cell transcription factor), ErbB4 (HER4), and vitamin-K-dependent plasma protein S (PROS1), an anticoagulation protein that prevents blood clots. Zinc inhibited the cleavage of these host sequences and in virus-infected cells; its cleavage could be inhibited by treating the cells with a cysteine protease inhibitor.1 TRIM14 has been proposed to be a component of the mitochondrial antiviral signalosome (MAVS).10 Here we refine and apply our methods to identify the potential targets of viral proteases from two Group IV viruses with distinct phenotypes, Zika and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We hypothesize that there may be a correlation between the proteases targets and the virus-induced phenotypes. Table 1 Host Protein Sequences That Have Been Reported to Be Cleaved by Group IV and VI Viral Proteases Open in a separate windows Many Group IV viral enzymes are produced compactly on a single nonstructural (ns) polyprotein, which is usually proteolyzed to release the active enzymes. Each ns protein (nsP) can contain multiple enzymes and domains strung together, and thus, a localization signal in one domain name can enable a linked enzyme to enter into an unexpected location such as the nucleus.11 In coronaviruses, the papain-like protease (PLpro) of nsP3 is anchored to the endoplasmic reticulum (ER) membrane around the IL1-BETA cytoplasmic face, and cleavage of host proteins may PU-WS13 occur co-translationally or post-translationally; nsP3 is also involved in inducing double membrane vesicles.12 Short stretches of homologous host-pathogen sequences (SSHHPS) can be found at the viral protease cleavage sites.1 Group IV viruses appear to mount a targeted attack on the host by destroying strategic proteins, enabling them to transiently impair the hosts immune responses to enable viral replication (Table 1). Notably, some of the host proteins are targeted by more than one viral protease, suggesting that they are PU-WS13 not randomly selected sequences. Several of the proteins listed are components of the MAVS (Physique S1) and Toll-like receptor pathways; cleavage of various components may short-circuit these cascades at different points. CRISPR/Cas systems embed short viral sequences in a hosts genome to protect a host from a computer virus, whereas SSHHPS/nsP systems appear to embed host or host-like sequences in the viral polyprotein in order to safeguard the virus from the host. Both are defense systems and can be viewed as sequence-specific silencing mechanisms1 (Physique ?Physique11). Open in a separate window Physique 1 Sequence-directed targeted cleavages. Silencing can occur at the level of DNA, RNA, or protein. Each PU-WS13 of these silencing mechanisms utilizes short sequences to direct cleavage of a larger target(s). In CRISPR/Cas systems, short pieces of viral sequences are embedded in the host genome, whereas in SSHHPS/nsP, short pieces of host or hostlike sequences can be found in the viral protease cleavage sites. These antagonistic mechanisms can be seen as search programs, in which the short sequence functions as a keyword and the target is a file (made up of the search term) that is cut. Each has an enzyme that searches for the match between the short sequence and the sequence in the file and then cleaves the target. SSHHPS/nsP is an example of a sequence-specific post-translational silencing mechanism that is transient.1 The CRISPR/Cas9 and RNAi figures have been adapted from refs (108) and (109)..
