9ma6
Crystal Structure of SARS-CoV-2 Main Protease (Mpro) Mutant del23T45I in Complex with Nirmatrelvir (P21 space group)
Structural highlights
FunctionR1A_SARS2 Multifunctional protein involved in the transcription and replication of viral RNAs. Contains the proteinases responsible for the cleavages of the polyprotein.[UniProtKB:P0C6X7] Inhibits host translation by interacting with the 40S ribosomal subunit. The nsp1-40S ribosome complex further induces an endonucleolytic cleavage near the 5'UTR of host mRNAs, targeting them for degradation. Viral mRNAs are not susceptible to nsp1-mediated endonucleolytic RNA cleavage thanks to the presence of a 5'-end leader sequence and are therefore protected from degradation. By suppressing host gene expression, nsp1 facilitates efficient viral gene expression in infected cells and evasion from host immune response.[UniProtKB:P0C6X7] May play a role in the modulation of host cell survival signaling pathway by interacting with host PHB and PHB2. Indeed, these two proteins play a role in maintaining the functional integrity of the mitochondria and protecting cells from various stresses.[UniProtKB:P0C6X7] Responsible for the cleavages located at the N-terminus of the replicase polyprotein. In addition, PL-PRO possesses a deubiquitinating/deISGylating activity and processes both 'Lys-48'- and 'Lys-63'-linked polyubiquitin chains from cellular substrates. Participates together with nsp4 in the assembly of virally-induced cytoplasmic double-membrane vesicles necessary for viral replication. Antagonizes innate immune induction of type I interferon by blocking the phosphorylation, dimerization and subsequent nuclear translocation of host IRF3. Prevents also host NF-kappa-B signaling.[UniProtKB:P0C6X7] Participates in the assembly of virally-induced cytoplasmic double-membrane vesicles necessary for viral replication.[UniProtKB:P0C6X7] Cleaves the C-terminus of replicase polyprotein at 11 sites. Recognizes substrates containing the core sequence [ILMVF]-Q-|-[SGACN]. Also able to bind an ADP-ribose-1-phosphate (ADRP).[UniProtKB:P0C6X7] Plays a role in the initial induction of autophagosomes from host reticulum endoplasmic. Later, limits the expansion of these phagosomes that are no longer able to deliver viral components to lysosomes.[UniProtKB:P0C6X7] Forms a hexadecamer with nsp8 (8 subunits of each) that may participate in viral replication by acting as a primase. Alternatively, may synthesize substantially longer products than oligonucleotide primers.[UniProtKB:P0C6X7] Forms a hexadecamer with nsp7 (8 subunits of each) that may participate in viral replication by acting as a primase. Alternatively, may synthesize substantially longer products than oligonucleotide primers.[UniProtKB:P0C6X7] May participate in viral replication by acting as a ssRNA-binding protein.[UniProtKB:P0C6X7] Plays a pivotal role in viral transcription by stimulating both nsp14 3'-5' exoribonuclease and nsp16 2'-O-methyltransferase activities. Therefore plays an essential role in viral mRNAs cap methylation.[UniProtKB:P0C6X7] Publication Abstract from PubMedSARS-CoV-2 variants resistant to current antivirals remain a significant threat, particularly in high-risk patients. Although nirmatrelvir and ensitrelvir both target the viral 3CL protease (M(pro)), their distinct susceptibility profiles may allow alternative therapeutic approaches. Here, we identify a deletion mutation at glycine 23 (Delta23G) in M(pro) that conferred high-level resistance to ensitrelvir ( ~ 35-fold) while paradoxically increasing susceptibility to nirmatrelvir ( ~ 8-fold). This opposite susceptibility pattern is confirmed both in vitro and in a male hamster infection model. Recombinant viruses carrying M(pro)-Delta23G exhibit impaired replication, pathogenicity, and transmissibility compared to wild-type, though the co-occurring mutation T45I partially restore viral fitness. Structural analyses reveal critical conformational changes in the catalytic loop (Ile136-Val148) and beta-hairpin loop (Cys22-Thr26), directly influencing inhibitor binding selectivity. These results highlight differential resistance profiles of M(pro) inhibitors, supporting potential sequential or alternative use of nirmatrelvir and ensitrelvir in patients requiring prolonged antiviral treatment. A SARS-CoV-2 M(pro) mutation conferring ensitrelvir resistance paradoxically increases nirmatrelvir susceptibility.,Min SC, Seo JJ, Jeong JH, Kim BK, Park JH, Lee JR, Lee DG, Lee GC, An SH, Baek YH, Choi YK, Choo H, Park HY, Kim G, Jeon B, Shin SC, Song MS Nat Commun. 2025 Nov 22;16(1):10737. doi: 10.1038/s41467-025-65767-z. PMID:41274896[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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