Human coronavirus OC43 3C-like protease (3CLpro) (3CLpro)

Human coronavirus OC43 3C-like protease (3CLpro), also known as the main protease (Mpro) or non-structural protein 5 (nsp5), is an essential enzyme for the replication of hCoV-OC43, a betacoronavirus associated with the common cold and occasionally severe respiratory disease (UniProt P0C6X6). This cysteine protease mediates the site-specific cleavage of viral polyproteins pp1a and pp1ab at 11 distinct sites, releasing functional non-structural proteins that form the viral replication-transcription complex (PubMed: 26001557). Because 3CLpro possesses a unique substrate specificity—cleaving after a glutamine residue—that is not shared by any known human host cell proteases, it is considered a high-priority therapeutic target for antiviral development (PubMed: 32454408). Therapeutic agents such as nirmatrelvir and experimental inhibitors like GC376 target the catalytic cysteine residue (Cys145) within the active site, effectively blocking viral maturation (PubMed: 33106344). While hCoV-OC43 is often used as a surrogate in research for highly pathogenic coronaviruses like SARS-CoV-2, its 3CLpro remains a direct target for treating infections in immunocompromised individuals where OC43 can cause life-threatening pneumonia (PubMed: 35105572). The enzyme functions as a homodimer, and its activity is crucial for the viral life cycle, making it a focus for pan-coronavirus drug discovery efforts. Inhibition of this target prevents the formation of the replication machinery, thereby stopping the production of new viral particles.

Other names

Main proteaseMproNon-structural protein 5nsp5hCoV-OC43 Mpro

Inhibition of the viral cysteine protease activity, preventing the cleavage of polyproteins pp1a and pp1ab into functional non-structural proteins, thereby halting viral replication.