Fluoxetine targets an allosteric site in the enterovirus 2C AAA+ ATPase and stabilizes the hexameric complex

The enterovirus genus encompasses many clinically important human pathogens such as poliovirus, coxsackieviruses, echoviruses, numbered enteroviruses and rhinoviruses. These viruses are the etiological agents of several human diseases, including hand-foot-and-mouth disease, neonatal sepsis, encephalitis, meningitis, paralysis and respiratory infections. There is an unmet need for antivirals to treat these diseases. The non-structural protein 2C is a AAA+ helicase and plays a key role in viral replication. As such, it is an attractive target for antiviral drug development. Several repurposing screens with FDA-approved drugs have identified 2C-targeting compounds such as fluoxetine and dibucaine, but the molecular basis of 2C inhibition has remained enigmatic. Here we present the 1.5 [A] resolution crystal structure of the soluble fragment of coxsackievirus B3 2C protein in complex with (S)-fluoxetine (SFX), which reveals a conserved, hydrophobic drug-binding pocket which is distal to the ATP binding site. To decipher the molecular mechanism of inhibition by fluoxetine and other 2C-targeting compounds, we engineered a soluble, hexameric and ATPase competent 2C protein. Using this system, we show that SFX, dibucaine, HBB and guanidine hydrochloride inhibit 2C ATPase activity in a dose-dependent manner. Moreover, using cryo-EM analysis, we demonstrate that SFX and dibucaine lock 2C in a defined hexameric state, rationalizing their mode of inhibition and allowing us to generate the first reconstruction of the oligomeric complex. Taken together, these results provide important structural and mechanistic insights into 2C inhibition and provide a robust engineering strategy which can be used for structural, functional and drug-screening analysis of 2C proteins from current or future enteroviruses.