Recognition and Cleavage of Human tRNA Methyltransferase TRMT1 by the SARS‐CoV‐2 Main Protease

Abstract

The SARS‐CoV‐2 main protease (MPro) is responsible for cleaving viral polypeptides to generate functional viral proteins, but like other viral proteases, MPro may also actively target and cleaave endogenous human host proteins during infection. Here we show that a human tRNA methyltransferase, TRMT1, can be recognized and cleaved by SARS‐CoV‐2 MPro. TRMT1 is a SAM‐dependent methyltransferase that installs the N 2,N 2‐dimethylguanosine (m2,2G) modification onto position G26 of human tRNAs. This abundant m2,2G modification is important for global protein synthesis, cellular redox homeostasis, and has been linked to neurodevelopmental defects. Early in the COVID‐19 pandemic, a host‐virus protein interaction map identified a putative interaction between SARS‐CoV‐2 MPro and human TRMT1. We carried out kinetic assays that show both a short peptide sequence in TRMT1 as well as endogenous, full‐length TRMT1 are actively cleaved by recombinant SARS‐CoV‐2 MPro in vitro. Cleavage of full‐length TRMT1 results in loss of its C‐terminal zinc finger domain thought to be critical for tRNA binding. Furthermore, we determined the co‐crystal structure of the human TRMT1 peptide in complex with SARS‐CoV‐2 MPro, which shows that the bound TRMT1 peptide substrate adopts a unique conformation in the protease active site. These results suggest that tRNA methyltransferase TRMT1 is a viable substrate for SARS‐CoV‐2 MPro, provide new structural insights into the diverse substrate recognition properties of the viral protease, and raise the possibility that TRMT1 cleavage during SARS‐CoV‐2 infection could contribute to downregulation of host protein synthesis or other phenotypes of viral infection.