Current projects
4) Gammaherpesviruses
We have ongoing collaborative projects investigating Kaposi's sarcoma-associated herpesvirus and Epstein-Barr virus, both of which belong to the Gammaherpesvirinae subfamily of Herpesviridae.
4.1) In situ atomic structures of the Kaposi's sarcoma-associated herpesvirus portal-terminase complex and glycoproteins
Kaposi's sarcoma-associated herpesvirus (KSHV) causes several types of cancer, including lymphomas and AIDS-associated malignancies. It is a member of the γ-herpesvirus subfamily of the Herpesviridae, and has been shown to be an etiologic agent of all forms of KS, primary effusion lymphoma, and multicentric Castleman's disease. Currently, no drugs specifically targeting lytic replication of KSHV are available.
Additionally, atomic structures of KSHV viral genome packaging/ejection machinery and fusion-mediating glycoproteins needed for rational design of antiviral drugs and vaccines are unavailable. Our recent work has led to the publication of the atomic structure of the KSHV capsid in Nature. Additionally, in collaboration with Prof. Ting-Ting Wu’s research group at UCLA, we have published the first atomic model of the KSHV DNA-packaging portal complex and capsid associated tegument complexes in Cell.
In our ongoing collaboration, we have established the feasibility of obtaining in situ structures of genome-packaging portal-terminase complex and the cell-entry glycoprotein B (gB) in both pre-fusion and post-fusion conformations. These portal protein and envelope glycoprotein structures and structure-guided mutagenesis results have led to three hypotheses:
(1) the portal-associated proteins and terminase interactions are vital to KSHV genome encapsidation;
(2) the interactions and conformational changes among envelope glycoproteins are required for KSHV fusion with host cells during cell entry; and
(3) such interactions revealed in atomic structures can help design inhibitors and vaccines against KSHV lytic infection. By taking advantage of technological breakthroughs in high-resolution cryoEM and KSHV mutagenesis, we aim to: (1) determine the in situ structures of KSHV portal-associated proteins and the terminase to ~3 Å by cryoEM and identify amino-acid residues vital to DNA packaging and ejection; (2) determine the structures of the pre-fusion and post-fusion states of gB and the interactions of gH/gL, gM/gN, and K8.1A with their binding partners; (3) refine our structural interpretation through structure-guided mutagenesis and identify target sites for inhibition of genome encapsidation and membrane fusion.
Results from this research program will inform the future development of drugs and novel vaccines against KSHV infection and spread. The novel approach established will be generally applicable to other viruses and complexes.
4.2) Structure and function of Epstein-Barr virus protein complexes that trigger epithelial cell entry
Epstein-Barr virus (EBV) is a γ-herpesvirus that causes infectious mononucleosis and is associated with B cell and epithelial cell cancers. EBV is an enveloped virus and therefore requires the fusion of the viral and cellular membrane to infect cells. The specificity of cell infection and membrane fusion triggered by the virus is for B cell entry is governed by four viral glycoproteins (gH, gL, gB and gp42), whereas EBV entry into epithelial cells requires three viral glycoproteins (gH, gL, and gB).
The gB protein is thought to play the primary role in mediating membrane fusion, receiving activating signals from the other proteins after receptor binding to cells. The gH and gL proteins form a complex that also associates with gp42, and this three-way complex is necessary for binding receptors on B cells and triggering their infection. However, for epithelial cells, gHgL interacts directly with EphA2 triggering EBV membrane fusion and entry, presumably by activating gB.
These "triggering" complexes of gHgL and cellular receptors are critically important for initiating EBV infection, but little is known about their structure and mechanism of action. In our ongoing collaboration with the research groups of Profs. Richard Jardetzky and Theordore Longnecker, we will study the architecture and mechanism of EBV epithelial cell triggering complexes, to gain greater insight into herpesvirus entry into cells. These studies may reveal general features of herpesvirus-mediated membrane fusion and open new possibilities for antiviral or vaccine development.
Select publications:
Structure and mutagenesis reveal essential capsid protein interactions for KSHV replication.
Dai, X., Gong, D., Lim, H., Jih, J., Wu, T.-T., Sun, R. & Zhou, Z. H. (2018) Nature
Dai, X., Gong, D., Lim, H., Jih, J., Wu, T.-T., Sun, R. & Zhou, Z. H. (2018) Nature
Structures of capsid and capsid-associated tegument complex inside the Epstein–Barr virus.
Liu, W., Cui, Y., Wang, C., Li, Z., Gong, D., Dai, X., Bi, G.-Q., Sun, R. & Zhou, Z. H. (2020). Nature Microbiology
Liu, W., Cui, Y., Wang, C., Li, Z., Gong, D., Dai, X., Bi, G.-Q., Sun, R. & Zhou, Z. H. (2020). Nature Microbiology
DNA-Packing Portal and Capsid-Associated Tegument Complexes in the Tumor Herpesvirus KSHV.
Gong, D., Dai, X., Jih, J., Liu, Y.-T., Bi, G.-Q., Sun, R. & Zhou, Z. H. (2019) Cell
Gong, D., Dai, X., Jih, J., Liu, Y.-T., Bi, G.-Q., Sun, R. & Zhou, Z. H. (2019) Cell