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Human norovirus GI.1 Norwalk protease in complex with rupintrivirHuman norovirus GI.1 Norwalk protease in complex with rupintrivir
Structural highlights
FunctionPOLG_NVN68 Protein p48 may play a role in viral replication by interacting with host VAPA, a vesicle-associated membrane protein that plays a role in SNARE-mediated vesicle fusion. This interaction may target replication complex to intracellular membranes.[1] [2] NTPase presumably plays a role in replication. Despite having similarities with helicases, does not seem to display any helicase activity.[3] [4] Protein P22 may play a role in targeting replication complex to intracellular membranes.[5] [6] Viral genome-linked protein is covalently linked to the 5'-end of the positive-strand, negative-strand genomic RNAs and subgenomic RNA. Acts as a genome-linked replication primer. May recruit ribosome to viral RNA thereby promoting viral proteins translation.[7] [8] 3C-like protease processes the polyprotein: 3CLpro-RdRp is first released by autocleavage, then all other proteins are cleaved. May cleave host polyadenylate-binding protein thereby inhibiting cellular translation (By similarity).[9] [10] RNA-directed RNA polymerase replicates genomic and antigenomic RNA by recognizing replications specific signals. Transcribes also a subgenomic mRNA by initiating RNA synthesis internally on antigenomic RNA. This sgRNA encodes for structural proteins. Catalyzes the covalent attachment VPg with viral RNAs (By similarity).[11] [12] Publication Abstract from PubMedHuman norovirus (HuNoV) is a leading cause of gastroenteritis worldwide and is associated with significant morbidity, mortality, and economic impact. There are currently no licensed antiviral drugs for the treatment of HuNoV-associated gastroenteritis. The HuNoV protease plays a critical role in the initiation of virus replication by cleaving the polyprotein. Thus, it is an ideal target for developing antiviral small-molecule inhibitors. While rupintrivir, a potent small-molecule inhibitor of several picornavirus proteases, effectively inhibits GI.1 protease, it is an order of magnitude less effective against GII protease. Other GI.1 protease inhibitors also tend to be less effective against GII proteases. To understand the structural basis for the potency difference, we determined the crystal structures of proteases of GI.1, pandemic GII.4 (Houston and Sydney), and GII.3 in complex with rupintrivir. These structures show that the open substrate pocket in GI protease binds rupintrivir without requiring significant conformational changes, whereas, in GII proteases, the closed pocket flexibly extends, reorienting arginine-112 in the BII-CII loop to accommodate rupintrivir. Structures of R112A protease mutants with rupintrivir, coupled with enzymatic and inhibition studies, suggest R112 is involved in displacing both substrate and ligands from the active site, implying a role in the release of cleaved products during polyprotein processing. Thus, the primary determinant for differential inhibitor potency between the GI and GII proteases is the increased flexibility in the BII-CII loop of the GII proteases caused by the H-G mutation in this loop. Therefore, the inherent flexibility of the BII-CII loop in GII proteases is a critical factor to consider when developing broad-spectrum inhibitors for HuNoV proteases. IMPORTANCE: Human noroviruses are a significant cause of sporadic and epidemic gastroenteritis worldwide. There are no vaccines or antiviral drugs currently available to treat infections. Our work elucidates the structural differences between GI.1 and GII proteases in response to inhibitor binding and will inform the future development of broad-spectrum norovirus protease inhibitors. Conformational flexibility is a critical factor in designing broad-spectrum human norovirus protease inhibitors.,Pham S, Zhao B, Neetu N, Sankaran B, Patil K, Ramani S, Song Y, Estes MK, Palzkill T, Prasad BVV J Virol. 2025 Jan 28:e0175724. doi: 10.1128/jvi.01757-24. PMID:39873493[13] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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