We study the molecular and structural biology of retroviruses, with particular emphasis on the Human Immunodeficiency Virus (HIV). As summarized below, major projects in the laboratory include studies of: 1) Enveloped virus assembly, 2) ESCRT pathway functions in cell division, and 3) HIV replication and restriction. Our approaches include structural studies of viral complexes, identification and biochemical analyses of the interactions between viral components and their cellular partners, and genetic analyses of viral and cellular protein functions. We currently have active collaborations in these different areas with the University of Utah labs of Nels Elde, Chris Hill and Katie Ullman, and with Adam Frost (UCSF), Neil King (University of Washington) and Juan Martin-Serrano (Kings College, London)
Enveloped Virus Assembly
To spread infections, HIV must form enveloped spherical particles that bud through the plasma membrane. We previously showed that HIV and other retroviruses bud from cells by usurping the activity of the host ESCRT pathway (Endosomal Sorting Pathway Required for Transport). More recently, we have discovered that HIV also usurps host proteins of the Angiomotin family to facilitate membrane envelopment prior to ESCRT-mediated budding. Our current work in this area focuses on: 1) understanding the molecular mechanism of HIV assembly and budding, 2) designing and characterizing new proteins that can exit and enter cells following the principles of enveloped viruses, and 3) testing how innate immune proteins can restrict viral use of the ESCRT pathway.
ESCRT Pathway Functions in Cell Division
In addition to functioning in enveloped virus budding, the ESCRT pathway also catalyzes a variety of different cellular membrane fission reactions, including during multivesicular body biogenesis, neuronal pruning, reassembly of the post-mitotic nuclear envelope, and the final stage of cell division (termed abscission). We, and others, have shown that the ESCRT pathway mediates the final mechanical step of cytokinetic abscission, recruits and organizes a number of other activities required for abscission, and helps coordinate the abscission/NoCut checkpoint, which delays completion of abscission until mitotic processes are complete and chromosomes have cleared the intercellular bridge. These fundamental processes are essential for development and can go awry in cancer. We are currently studying how the ESCRT pathway mediates and regulates abscission, including determining: 1) the structures and functions of the constricting filaments formed by the ESCRT-III proteins, 2) how those filaments recruit other proteins and their enzymatic activities to the nascent intercellular bridge, and 3) the signaling pathways that govern the abscission checkpoint and regulate ESCRT activity.
HIV Replication and Restriction
HIV capsids facilitate reverse transcription and protect the viral genome from innate immune systems, but are also themselves the targets of host immune restriction factors. We have previously defined the structure of the HIV capsid and shown how the host restriction factor TRIM5α recognizes and assembles around the capsid. We are now studying: 1) how the capsid promotes reverse transcription, and 2) how TRIM5α binding inhibits this process.