Proteolytic processing of viral polyproteins is essential for retrovirus infectivity. Retroviral proteases (PR) become activated during or after assembly of the immature, non-infectious virion. They cleave viral polyproteins at specific sites, inducing major structural rearrangements termed maturation. Maturation converts retroviral enzymes into their functional form, transforms the immature shell into a metastable state primed for early replication events, and enhances viral entry competence. Not only cleavage at all PR recognition sites, but also an ordered sequence of cleavages is crucial. Proteolysis is tightly regulated, but the triggering mechanisms and kinetics and pathway of morphological transitions remain enigmatic. Here, we outline PR structures and substrate specificities focusing on HIV PR as a therapeutic target. We discuss design and clinical success of HIV PR inhibitors, as well as resistance development towards these drugs. Finally, we summarize data elucidating the role of proteolysis in maturation and highlight unsolved questions regarding retroviral maturation.

Department of Infectious Diseases Virology University Hospital Heidelberg Im Neuenheimer Feld 324 69120 Heidelberg Germany; Molecular Medicine Partnership Unit Heidelberg Germany

Institute of Organic Chemistry and Biochemistry Academy of Sciences of the Czech Republic Gilead Sciences and IOCB Research Center Flemingovo n 2 166 10 Prague 6 Czech Republic; Department of Biochemistry Faculty of Science Charles University Prague Hlavova 8 128 43 Prague 2 Czech Republic

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