Targeting Viral Precursor Proteases for Innovative Therapeutic Development

Proteolytic processing of viral polyproteins by virally encoded proteases is essential for the replication of many RNA viruses, including retroviruses and coronaviruses, which are two of the best characterized model systems discussed in this review. These proteases are initially synthesized as polyprotein precursors that possess intrinsic, albeit comparatively low, catalytic activity and undergo tightly regulated autoprocessing to generate the mature enzymes required for viral replication. Accumulating evidence indicates that protease precursors are catalytically and mechanistically distinct from their mature counterparts, exhibiting unique biochemical properties and regulatory features that govern their activation. Therefore, precursor autoprocessing represents a critical checkpoint in viral maturation and an attractive, yet largely unexplored, target for antiviral intervention. This review examines the current understanding of the molecular mechanisms underlying precursor autoprocessing of HIV-1 protease and coronavirus main protease, with particular emphasis on the structural, biochemical, and regulatory features that distinguish precursor enzymes from their mature forms. It also highlights the experimental challenges associated with studying these highly dynamic and conformationally heterogeneous precursors, as well as recent advances in functional screening platforms that have enabled the discovery of proof-of-concept small molecules targeting precursor autoprocessing. Notably, several hit compounds retain activity against HIV-1 variants resistant to clinically approved protease inhibitors (PIs), while also inhibiting the wild-type strain. Together, these findings suggest that protease precursor autoprocessing may serve as a promising antiviral target and provide a conceptual framework for the development of next-generation therapeutics that complement existing mature-protease inhibitors.