Flavivirus NS4B protein: Structure, function, and antiviral discovery

Abstract

Infections with mosquito-borne flaviviruses, such as Dengue virus, ZIKV virus, and West Nile virus, pose significant threats to public health. Flaviviruses cause up to 400 million infections each year, leading to many forms of diseases, including fatal hemorrhage, encephalitis, congenital abnormalities, and deaths. Currently, there are no clinically approved antiviral drugs for the treatment of flavivirus infections. The non-structural protein NS4B is an emerging target for drug discovery due to its multiple roles in the flaviviral life cycle. In this review, we summarize the latest knowledge on the structure and function of flavivirus NS4B, as well as the progress on antiviral compounds that target NS4B.

Keywords: Antivirals; Drug discovery; Flavivirus; Nonstructural protein 4B.

Figure 1.

Sequence alignment, membrane topology, and structure model of flavivirus NS4B protein. (A) Sequence alignment of NS4B proteins from DENV-1 to −4, ZIKV, JEV, WNV, YFV, and TBEV. The helices α1 to α9 are labeled according to the NMR results. The resistance mutations against different NS4B inhibitors (i.e., Compound 14, NITD-618, NITD-688, JNJ-A07, and BDAA) are labeled with different colors. See details in the main text. (B) AlphaFold2 model of DENV-2 NS4B. The color is labeled as that in (A). (C) Membrane topology of DENV-2 NS4B based on the NMR probed full-length NS4B structure and AlphaFold2 model. The color is labeled as that in (A) and (B).

Figure 2.

The functions of flavivirus NS4B protein in the viral life cycle. After release from the polypeptide by NS3 and host signalase, NS4B recruits host protein to alter the membrane topology of ER and facilitates the formation of viral replication complex by interacting with other viral proteins. Besides viral replication, NS4B also functions in counteracting the host innate immune responses and inducing cell dysregulation by blocking type I IFN signaling, inhibiting RNAi pathway, suppressing the formation of stress granules, and induing autophagy and apoptosis.