# Roles of KSHV Tegument Proteins in Virion Assembly

> **NIH NIH R01** · UNIVERSITY OF PENNSYLVANIA · 2022 · $407,339

## Abstract

Summary
Kaposi's sarcoma-associated herpesvirus (KSHV) is an etiological agent of Kaposi's sarcoma (KS), primary
effusion lymphoma (PEL) and multicentric Castleman's disease (MCD). Lytic KSHV replication is crucial to
tumorogenicity because in KS lesions it sustains the population of latently infected cells that would otherwise
be lost by segregation of latent viral episomes as spindle cells divide. Despite the importance of lytic replication
in viral pathogenesis, many processes of KSHV lytic life cycle, especially the roles of tegument proteins in
virion assembly, remain poorly understood, partly due to the technical challenges inherent in studying such
complex, host-related and membrane-associated processes. Through over a decade of efforts, the two
collaborating groups of this application have overcome many technical hurdles and obtained a large body of
preliminary data on KSHV structure and assembly. Our persistent efforts, though characterized by slow
progress, has paved the road finally for rapid progress towards a thorough understanding of KHSV virion
assembly. For example, the Yuan group used state-of-the-art proteomics and systems biology approaches to
analyze KSHV virion protein composition and to draw a virion-wide protein interaction map. The Zhou lab has
advanced cryo electron microscopy (cryoEM) and cryo electron tomography (cryoET) to visualize both ordered
and pleomorphic (disordered) components of large viruses at near-atomic resolution and molecular resolution,
respectively. These efforts have led to our hypotheses concerning the roles of the largest tegument protein
ORF64 and a KSHV-specific tegument protein ORF45: (i) ORF64 interacts with the capsid through its C-
terminal end helix bundle and connects ORF45 at its other end; (ii) tegumented KSHV capsids are transported
from nuclear periphery to the trans-Golgi network (TGN) through ORF45-mediated movement along
microtubules; (iiI) ORF64 guides the particles to TGN membrane where viral glycoproteins are present; and (iv)
ORF45 promotes internalization of viral particles into TGN vesicles for final envelopment through a mono-
ubiquitin-mediated recognition by cellular membrane sorting machinery. The proposed studies harnesses our
complementary expertise to test these hypotheses. Our three specific aims are: (1) We will establish the
structural basis of ORF45 and ORF64 to target lipid rafts and to bind viral glycoproteins by determining in situ
tegument organization in the virion by cryoET and near-atomic resolution structure of the ordered domains
ORF64 in tegumented capsids by cryoEM; (2) Guided by structure data, molecular biology approaches will be
utilized to define the roles of ORF64 in virion envelopment and egress at the Golgi-derived vesicles; (3) By an
integrative approach of molecular biology and 3D correlative photon/electron microscopy, we will elucidate the
mechanism of ORF45-mediated targeting and internalization of viral particles into the lumen of TGN vesicles....

## Key facts

- **NIH application ID:** 10480736
- **Project number:** 5R01DE027901-05
- **Recipient organization:** UNIVERSITY OF PENNSYLVANIA
- **Principal Investigator:** Chi-Der Chen
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2022
- **Award amount:** $407,339
- **Award type:** 5
- **Project period:** 2018-04-02 → 2025-03-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10480736

## Citation

> US National Institutes of Health, RePORTER application 10480736, Roles of KSHV Tegument Proteins in Virion Assembly (5R01DE027901-05). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/10480736. Licensed CC0.

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