SARS-CoV-2 3C-like protease (3CLpro) (3CLpro)

The SARS-CoV-2 3C-like protease (3CLpro), also known as the main protease (Mpro), is a cysteine protease essential for the life cycle of the SARS-CoV-2 virus [UniProt P0DTD1]. It is initially synthesized as part of the large replicase polyproteins 1a (pp1a) and 1ab (pp1ab) [Jin et al., Nature 2020]. The enzyme's primary biological role is to cleave these polyproteins at eleven specific sites to release functional non-structural proteins (nsps), which are vital for viral RNA replication and transcription [Zhang et al., Science 2020]. Because 3CLpro recognizes a specific cleavage sequence that is not utilized by human host cell proteases, it serves as a highly selective target for antiviral therapy [Owen et al., Science 2021]. Drugs such as nirmatrelvir and ensitrelvir function by binding to the active site of 3CLpro, often forming a covalent bond with the catalytic Cys145 residue, thereby preventing the maturation of the viral replication complex [FDA Paxlovid Label]. This inhibition effectively stops viral proliferation within the host, leading to reduced viral loads and improved clinical outcomes in patients with COVID-19 [Hammond et al., NEJM 2022]. Therapeutic challenges include the management of significant drug-drug interactions when the inhibitor is co-administered with pharmacokinetic enhancers like ritonavir, as well as monitoring for the emergence of resistant viral variants [NIH COVID-19 Guidelines].

Other names

Main proteaseMproNon-structural protein 5nsp5SARS-CoV-2 3CL protease

Inhibition of the viral main protease (Mpro/3CLpro), which prevents the cleavage of polyproteins 1a and 1ab into functional non-structural proteins, thereby halting viral replication.