Institut de Biologie StructuraleGrenoble / France

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Activation of Epstein-Barr virus lytic infection

Epstein-Barr Virus (EBV) is a human herpesvirus that infects over 90% of the world population. EBV causes infectious mononucleosis and is associated with diverse malignancies, including Hodgkin’s disease, Burkitt’s lymphoma, nasopharyngeal carcinoma, and lymphomas in immunocompromised individuals such as AIDS patients and organ transplant recipients. EBV persists in most individuals as a lifelong, asymptomatic infection of B lymphocytes. Infection is primarily latent, but EBV periodically reactivates and replicates in a lytic manner in a subset of B cells – a form of infection essential for viral propagation and transmission.

The Lytic Switch Protein

The switch from latency to lytic infection is triggered by the EBV immediate-early transcription factor ZEBRA (BZLF1, Zta, Z, EB1). ZEBRA is a multifunctional protein that activates EBV lytic genes, represses latency-associated promoters, is an essential replication factor, interferes with the host cell cycle, alters immune responses and modulates cellular transcription factor activity. ZEBRA is an attractive drug target because the lytic cycle is completely disrupted when ZEBRA expression is inhibited or its activity compromised.

Our crystal structure of ZEBRA’s DNA-binding domain revealed a novel variant of the basic region leucine zipper (bZIP) fold, characterized by a unique dimer interface with a deep hydrophobic pocket. The structure demonstrated that ZEBRA is “druggable” and that its dimer interface contains an obvious hot spot on which to focus efforts at rational inhibitor design.

Research Goals

Current work is aimed at better understanding how ZEBRA initiates and maintains the viral lytic cycle. This includes how ZEBRA achieves broad target site specificity and how it preferentially activates methylated promoters to overcome latency-associated epigenetic silencing of the EBV genome. Another goal is to identify small molecules that inhibit ZEBRA from dimerizing and binding DNA. Such compounds should facilitate the development of new therapeutic agents that block EBV lytic cycle activation

Crystal structure of ZEBRA bound to DNA. Also shown are a B lymphocyte latently infected by EBV (left), and a B cell lysed by the replicating virus. In the background is an electron microscopic image of infectious viral particles.

Dimer interface of ZEBRA. The hydrophobic pocket indicated by the asterisk is a potential target for rational drug design.