Defining substrate selection by rhinoviral 2A proteinase through its crystal structure with the inhibitor zVAM.fmk.

Picornavirus family members cause disease in humans. Human rhinoviruses (RV), the main causative agents of the common cold, increase the severity of asthma and COPD; hence, effective agents against RVs are required. The 2A proteinase (2Apro), found in all enteroviruses, represents an attractive target; inactivating mutations in poliovirus 2Apro result in an extension of the VP1 protein preventing infectious virion assembly. Variations in sequence and substrate specificity on eIF4G isoforms between RV 2Apro of genetic groups A and B hinder 2Apro as drug targets. Here, we demonstrate that although RV-A2 and RV-B4 2Apro cleave the substrate GAB1 at different sites, the 2Apro from both groups cleave equally efficiently an artificial site containing P1 methionine. We determined the RV-A2 2Apro structure complexed with zVAM.fmk, containing P1 methionine. Analysis of this first 2Apro-inhibitor complex reveals a conserved hydrophobic P4 pocket among enteroviral 2Apro as a potential target for broad-spectrum anti-enteroviral inhibitors.

Dissecting distinct proteolytic activities of FMDV Lpro implicates cleavage and degradation of RLR signaling proteins, not its deISGylase/DUB activity, in type I interferon suppression.

The type I interferon response is an important innate antiviral pathway. Recognition of viral RNA by RIG-I-like receptors (RLRs) activates a signaling cascade that leads to type I interferon (IFN-α/ß) gene transcription. Multiple proteins in this signaling pathway (e.g. RIG-I, MDA5, MAVS, TBK1, IRF3) are regulated by (de)ubiquitination events. Most viruses have evolved mechanisms to counter this antiviral response. The leader protease (Lpro) of foot-and-mouth-disease virus (FMDV) has been recognized to reduce IFN-α/ß gene transcription; however, the exact mechanism is unknown. The proteolytic activity of Lpro is vital for releasing itself from the viral polyprotein and for cleaving and degrading specific host cell proteins, such as eIF4G and NF-κB. In addition, Lpro has been demonstrated to have deubiquitination/deISGylation activity. Lpro's deubiquitination/deISGylation activity and the cleavage/degradation of signaling proteins have both been postulated to be important for reduced IFN-α/ß gene transcription. Here, we demonstrate that TBK1, the kinase that phosphorylates and activates the transcription factor IRF3, is cleaved by Lpro in FMDV-infected cells as well as in cells infected with a recombinant EMCV expressing Lpro. In vitro cleavage experiments revealed that Lpro cleaves TBK1 at residues 692-694. We also observed cleavage of MAVS in HeLa cells infected with EMCV-Lpro, but only observed decreasing levels of MAVS in FMDV-infected porcine LFPK αVß6 cells. We set out to dissect Lpro's ability to cleave RLR signaling proteins from its deubiquitination/deISGylation activity to determine their relative contributions to the reduction of IFN-α/ß gene transcription. The introduction of specific mutations, of which several were based on the recently published structure of Lpro in complex with ISG15, allowed us to identify specific amino acid substitutions that separate the different proteolytic activities of Lpro. Characterization of the effects of these mutations revealed that Lpro's ability to cleave RLR signaling proteins but not its deubiquitination/deISGylation activity correlates with the reduced IFN-ß gene transcription.

A novel non-canonical PIP-box mediates PARG interaction with PCNA.

Poly(ADP-ribose) glycohydrolase (PARG) regulates cellular poly(ADP-ribose) (PAR) levels by rapidly cleaving glycosidic bonds between ADP-ribose units. PARG interacts with proliferating cell nuclear antigen (PCNA) and is strongly recruited to DNA damage sites in a PAR- and PCNA-dependent fashion. Here we identified PARG acetylation site K409 that is essential for its interaction with PCNA, its localization within replication foci and its recruitment to DNA damage sites. We found K409 to be part of a non-canonical PIP-box within the PARG disordered regulatory region. The previously identified putative N-terminal PIP-box does not bind PCNA directly but contributes to PARG localization within replication foci. X-ray structure and MD simulations reveal that the PARG non-canonical PIP-box binds PCNA in a manner similar to other canonical PIP-boxes and may represent a new type of PIP-box. While the binding of previously described PIP-boxes is based on hydrophobic interactions, PARG PIP-box binds PCNA via both stabilizing hydrophobic and fine-tuning electrostatic interactions. Our data explain the mechanism of PARG-PCNA interaction through a new PARG PIP-box that exhibits non-canonical sequence properties but a canonical mode of PCNA binding.

Interaction of 2A proteinase of human rhinovirus genetic group A with eIF4E is required for eIF4G cleavage during infection.

In enteroviruses, the inhibition of protein synthesis from capped host cell mRNA is catalyzed by the virally encoded 2A proteinase (2Apro), which cleaves eukaryotic initiation factors (eIF) 4GI and 4GII. Despite much investigation, the exact mechanism of 2Apro cleavage remains however unclear. Here, we identify the domains responsible for the eIF4E/HRV2 2Apro interaction using molecular modelling and describe mutations that impair this interaction and delay in vitro cleavage of eIF4G isoforms. Furthermore, we produced HRV1A viruses bearing the mutation L17R, Y32A or Y86A in the 2Apro sequence. All three viruses showed reduced yield and were appreciably delayed during infection in eIF4GI cleavage. Thus, we propose for genetic group A HRVs that the eIF4E/2Apro interaction is essential for successful viral replication. In contrast, HRV4 2Apro and coxsackievirus B4 2Apro failed to form complexes with eIF4E, suggesting that the mechanism of eIF4G isoform cleavage in these and related viruses is different.

Proteome-wide drug and metabolite interaction mapping by thermal-stability profiling.

Thermal stabilization of proteins after ligand binding provides an efficient means to assess the binding of small molecules to proteins. We show here that in combination with quantitative mass spectrometry, the approach allows for the systematic survey of protein engagement by cellular metabolites and drugs. We profiled the targets of the drugs methotrexate and (S)-crizotinib and the metabolite 2'3'-cGAMP in intact cells and identified the 2'3'-cGAMP cognate transmembrane receptor STING, involved in immune signaling.