X-domain (or Mac1 domain) of viral non-structural protein 3 and related macrodomains
The X-domain, also called Mac1, is the macrodomain found in riboviral non-structural protein 3 (Nsp3), including the Nsp3 of Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV) as well as SARS-CoV-2, and other coronaviruses (alpha-, beta-, gamma-, and deltacoronavirus), among others. The SARS-CoV-2 Nsp3 Mac1 is highly conserved among all CoVs, and binds to and hydrolyzes mono-ADP-ribose (MAR) from target proteins. It appears to counter host-mediated antiviral ADP-ribosylation, a post-translational modification that is part of the host response to viral infections. Mac1 is essential for pathogenesis in multiple animal models of CoV infection, implicating it as a virulence factor and potential therapeutic target. Assays show that the de-MARylating activity leads to a rapid loss of substrate, and that Mac1 could not hydrolyze poly-ADP-ribose; thus, Mac1 is a MAR-hydrolase (mono-ADP ribosylhydrolase). Mac1 was originally named ADP-ribose-1"-phosphatase (ADRP) based on data demonstrating that it could remove the phosphate group from ADP-ribose-1"-phosphate; however, activity was modest and was unclear why this would impact a virus infection. This family also includes the X-domain of Avian infectious bronchitis virus (IBV) strain Beaudette coronavirus that does not bind ADP-ribose; the triple glycine sequence found in the X-domains of SARS-CoV and human coronavirus 229E (HCoV229E), which are involved in ADP-ribose binding, is not conserved in the IBV X-domain. SARS-CoVs have two other macrodomains referred to as the SUD-N (N-terminal subdomain, or Mac2) and SUD-M (middle SUD subdomain, or Mac3) of the SARS-unique domain (SUD), which also do not bind ADP-ribose; these bind G-quadruplexes (unusual nucleic-acid structures formed by consecutive guanosine nucleotides). SARS-CoV SUD-N and SUD-M are not included in this group.
Feature 1:ADP-ribose binding site [chemical binding site]
Evidence:
Comment:not all macrodomains belonging to this family bind ADP-ribose, for example the X-domain of Avian infectious bronchitis virus (IBV) strain Beaudette coronavirus
Structure:6W02: SARS-CoV-2 Nsp3 macrodomain binds ADP-ribose; contacts at 4A
Jiyao W et al.(2023). "The conserved domain database in 2023.",