Gregory Melikian, PhD
Division of Infectious Disease
Department of Pediatrics
Emory University School of Medicine
2015 Uppergate Drive
Atlanta, GA, 30322
Our laboratory studies the molecular mechanisms of enveloped virus entry into cells. When activated by binding to cellular receptors and/or by acidic pH in endosomes, viral fusion proteins undergo extensive conformational changes resulting in membrane merger. Current projects involve function studies of fusion proteins of influenza virus, Human Immunodeficiency Virus (HIV) and other retroviruses, as well as Hepatitis C Virus (HCV). By imaging individual virions co-labeled with fluorescent membrane and content markers, we visualize the lipid mixing (hemifusion) and the fusion pore formation steps in live cells.
We have recently showed that HIV, which has long been thought to infect host cells by direct fusion with the plasma membrane, enters permissive cells via endocytosis and pH-independent fusion with endosomes. These findings provide a new paradigm for HIV entry and suggest alternative strategies to block infection. We also study the entry mechanisms of low pH-dependent viruses, influenza and Avian Sarcoma and Leukosis Virus (ASLV). ASLV Env glycoprotein is first primed by interactions with a cognate receptor at the cell surface, which renders Env competent for low pH-induced conformational changes and fusion with acidic endosomes. Sequential priming and triggering of ASLV fusion and the virus’ ability to utilize two naturally occurring isoforms of the cognate receptor is essential for dissecting the virus entry pathways. Our work on the mechanism of HCV fusion involves the usage of soluble receptor fragments and low pH to trap transient states of the HCV E1E2 glycoproteins en route to fusion with acidic endosomes. We have shown that one of the four essential receptors, CD81, renders HCV competent for low pH-mediated fusion within endosomes. Another project in the laboratory is aimed at understanding the anti-viral activity of human defensins, highly charged cationic peptides capable of blocking entry of HIV and other viruses.
We are currently applying quantitative imaging and spectroscopy methods to better understand virus trafficking and fusion, as well as to delineate the role of receptor signaling in infection. We are also interested in reconstituting viral fusion in a supported lipid bilayer system and carrying out mechanistic studies of this process on a single-molecule level.