The recent outbreak of Zika virus (ZIKV) infections in the Americas represents a serious threat to the global public health. The viral protease that processes viral polyproteins during infection appears as an attractive drug target. Here we report a crystal structure at 1.84 Å resolution of ZIKV non-structural protein NS2B-NS3 protease with the last four amino acids of the NS2B cofactor bound at the NS3 active site. This structure represents a post-proteolysis state of the enzyme during viral polyprotein processing and provides insights into peptide substrate recognition by the protease. Nuclear magnetic resonance (NMR) studies and protease activity assays unravel the protein dynamics upon binding the protease inhibitor BPTI in solution and confirm this finding. The structural and functional insights of the ZIKV protease presented here should advance our current understanding of flavivirus replication and accelerate structure-based antiviral drug discovery against ZIKV.

Zika virus (ZIKV) has rapidly emerged as a global public health concern. Viral NS2B-NS3 protease processes viral polyprotein and is essential for the virus replication, making it an attractive antiviral drug target. We report crystal structures at 1.58-angstrom resolution of the unlinked NS2B-NS3 protease from ZIKV as free enzyme and bound to a peptide reversely oriented at the active site. The unlinked NS2B-NS3 protease adopts a closed conformation in which NS2B engages NS3 to form an empty substrate-binding site. A second protease in the same crystal binds to the residues K14K15G16E17 from the neighboring NS3 in reverse orientation, resisting proteolysis. These features of ZIKV NS2B-NS3 protease may accelerate the discovery of structure-based antiviral drugs against ZIKV and related pathogenic flaviviruses.

The NS2B-NS3 viral protease is an attractive drug target against Zika virus (ZIKV) due to its importance in viral replication and maturation. Here we report the crystal structure of protease in complex with a dipeptide inhibitor, Acyl-KR-aldehyde (compound 1). The aldehyde moiety forms a covalent bond with the catalytic Ser of NS3. The Arg and Lys residues in the inhibitor occupy the S1 and S2 sites of the protease, respectively. Nuclear magnetic resonance studies demonstrate that the complex is in the closed conformation in solution. The chemical environment of residues surrounding the active site is sensitive to the bound inhibitor as demonstrated by the comparison with two other non-covalent dipeptides, Acyl-K-Agmatine (compound 2) and Acyl-KR-COOH (compound 3). Removing the aldehyde moiety in 1 converts the binding mode from a slow to a fast exchange regime. The structural dynamics information obtained in this study will guide future drug discovery against ZIKV and other flaviviruses.