An open conformation determined by a structural switch for 2A protease from coxsackievirus A16

Coxsackievirus A16 belongs to the family Picornaviridae,and is a major agent of hand-foot-and-mouth disease that infects mostly children,and to date no vaccines or antivi-ral therapies are available.2A protease of enterovirus is a nonstructural protein and possesses both self-cleavage activity and the ability to cleave the eukaryotic translation initiation factor 4G.Here we present the crystal structure of coxsackievirus A162A protease,which interestingly forms hexamers in crystal as well as in solution.This structure shows an open conformation,with its active site accessible,ready for substrate binding and cleav-age activity.In conjunction with a previously reported“closed”state structure of human rhinovirus 2,we were able to develop a detailed hypothesis for the conforma-tional conversion triggered by two“switcher”residues Glu88 and Tyr89 located within the bll2-cII loop.Substrate recognition assays revealed that amino acid residues P1′,P2 and P4 are essential for substrate specificity,which was verifi ed by our substrate binding model.In addition,we compared the in vitro cleavage effi ciency of 2A pro-teases from coxsackievirus A16 and enterovirus 71 upon the same substrates by fl uorescence resonance energy transfer(FRET),and observed higher protease activity of enterovirus 71 compared to that of coxsackievirus A16.In conclusion,our study shows an open conformation of coxsackievirus A162A protease and the underlying mechanisms for conformational conversion and substrate specifi city.These new insights should facilitate the future rational design of effi cient 2A protease inhibitors.

Baicalein suppresses Coxsackievirus B3 replication by inhibiting caspase-1 and viral protease 2A

Myocarditis is an inflammatory disease of the cardiac muscle and one of the primary causes of dilated cardiomyopathy.Group B coxsackievirus(CVB)is one of the leading causative pathogens of viral myocarditis,which primarily affects children and young adults.Due to the lack of vaccines,the development of antiviral medicines is crucial to controlling CVB infection and the progression of myocarditis.In this study,we investigated the antiviral effect of baicalein,a flavonoid extracted from Scutellaria baicaleinsis.Our results demonstrated that baicalein treatment significantly reduced cytopathic effect and increased cell viability in CVB3-infected cells.In addition,significant reductions in viral protein 3D,viral RNA,and viral particles were observed in CVB3-infected cells treated with baicalein.We found that baicalein exerted its inhibitory effect in the early stages of CVB3 infection.Baicalein also suppressed viral replication in the myocardium and effectively alleviated myocarditis induced by CVB3 infection.Our study revealed that baicalein exerts its antiviral effect by inhibiting the activity of caspase-1 and viral protease 2A.Taken together,our findings demonstrate that baicalein has antiviral activity against CVB3 infection and may serve as a potential therapeutic option for the myocarditis caused by enterovirus infection.

TAR DNA-Binding Protein 43 is Cleaved by the Protease 3C of Enterovirus A71

Enterovirus A71(EV-A71)is one of the etiological pathogens leading to hand,foot,and mouth disease(HFMD),which can cause severe neurological complications.The neuropathogenesis of EV-A71 infection is not well understood.The mislocalization and aggregation of TAR DNA-binding protein 43(TDP-43)is the pathological hallmark of amyotrophic lateral sclerosis(ALS).However,whether TDP-43 was impacted by EV-A71 infection is unknown.This study demonstrated that TDP-43 was cleaved during EV-A71 infection.The cleavage of TDP-43 requires EV-A71 replication rather than the activated caspases due to viral infection.TDP-43 is cleaved by viral protease 3 C between the residues 331 Q and332 S,while mutated TDP-43(Q331 A)was not cleaved.In addition,mutated 3 C which lacks the protease activity failed to induce TDP-43 cleavage.We also found that TDP-43 was translocated from the nucleus to the cytoplasm,and the mislocalization of TDP-43 was induced by viral protease 2 A rather than 3 C.Taken together,we demonstrated that TDP-43 was cleaved by viral protease and translocated to the cytoplasm during EV-A71 infection,implicating the possible involvement of TDP-43 in the pathogenesis of EV-A71 infection.