Mutation of Asn-475 in the Venezuelan Equine Encephalitis Virus nsP2 Cysteine Protease Leads to a Self-Inhibited State.Compton, J.R., Mickey, M.J., Hu, X., Marugan, J.J., Legler, P.M.
(2017) Biochemistry 56: 6221-6230
- PubMed: 29064679
- DOI: https://doi.org/10.1021/acs.biochem.7b00746
- Primary Citation of Related Structures:
- PubMed Abstract:
The alphaviral nsP2 cysteine protease of the Venezuelan equine encephalitis virus (VEEV) is a validated antiviral drug target. Clan CN proteases contain a cysteine protease domain that is intimately packed with an S-adenosyl-l-methionine-dependent RNA methyltransferase (SAM MTase) domain ...
The alphaviral nsP2 cysteine protease of the Venezuelan equine encephalitis virus (VEEV) is a validated antiviral drug target. Clan CN proteases contain a cysteine protease domain that is intimately packed with an S-adenosyl-l-methionine-dependent RNA methyltransferase (SAM MTase) domain. Within a cleft formed at the interface of these two domains, the peptide substrate is thought to bind. The nucleophilic cysteine can be found within a conserved motif, 475 NVCWAK 480 , which differs from that of papain ( 22 CGSCWAFS 29 ). Mutation of the motif residue, N475, to alanine unexpectedly produced a self-inhibited state in which the N-terminal residues flipped into the substrate-binding cleft. Notably, the N-terminal segment was not hydrolyzed-consistent with a catalytically incompetent state. The N475A mutation resulted in a 70-fold decrease in k cat /K m . A side chain-substrate interaction was predicted by the structure; the S701A mutation led to a 17-fold increase in K m . An Asn at the n-2 position relative to the Cys was also found in the coronaviral papain-like proteases/deubiquitinases (PLpro) of the SARS and MERS viruses, and in several papain-like human ubiquitin specific proteases (USP). The large conformational change in the N475A variant suggests that Asn-475 plays an important role in stabilizing the N-terminal residues and in orienting the carbonyl during nucleophilic attack but does not directly hydrogen bond the oxyanion. The state trapped in crystallo is an unusual result of site-directed mutagenesis but reveals the role of this highly conserved Asn and identifies key substrate-binding contacts that may be exploited by peptide-like inhibitors.
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