Human ddx3x unwinds Japanese encephalitis and zika viral 5՛ terminal regions

Abstract

Flavivirus genus includes many deadly viruses such as the Japanese encephalitis virus (JEV) and Zika virus (ZIKV). The 5՛ terminal regions (TR) of flaviviruses interact with human proteins and such interactions are critical for viral replication. One of the human proteins identified to interact with the 5՛ TR of JEV is the DEAD-box helicase, DDX3X. In this study, we in vitro transcribed the 50 TR of JEV and demonstrated its direct interaction with recombinant DDX3X (Kd of 1.66  0.21 μM) using microscale thermophoresis (MST). Due to the proposed structural similarities of 5՛ and 3՛ TRs of flaviviruses, we investigated if the ZIKV 50 TR could also interact with human DDX3X. Our MST studies suggested that DDX3X recognizes ZIKV 50 TR with a Kd of 7.05  0.75 μM. Next, we performed helicase assays that suggested that the binding of DDX3X leads to the unwinding of JEV and ZIKV 5՛ TRs. Overall, our data indicate, for the first time, that DDX3X can directly bind and unwind in vitro transcribed flaviviral TRs. In summary, our work indicates that DDX3X could be further explored as a therapeutic target to inhibit Flaviviral replication.