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

Enteroviruses are globally prevalent human pathogens responsible for many diseases. The nonstructural protein 2C is a AAA+ helicase and plays a key role in enterovirus replication. Drug repurposing screens identified 2C-targeting compounds such as fluoxetine and dibucaine, but how they inhibit 2C is unknown. Here, we present a crystal structure of the soluble and monomeric fragment of coxsackievirus B3 2C protein in complex with (S)-fluoxetine (SFX), revealing an allosteric binding site. To study the functional consequences of SFX binding, we engineered an adenosine triphosphatase (ATPase)-competent, hexameric 2C protein. Using this system, we show that SFX, dibucaine, HBB [2-(alpha-hydroxybenzyl)-benzimidazole], and guanidine hydrochloride inhibit 2C ATPase activity. Moreover, cryo-electron microscopy analysis demonstrated that SFX and dibucaine lock 2C in a defined hexameric state, rationalizing their mode of inhibition. Collectively, these results provide important insights into 2C inhibition and a robust engineering strategy for structural, functional, and drug-screening analysis of 2C proteins.