Principal Investigator/Program Director (Last, first, middle): AJken, Christopher R., Ph.D. DESCRIPTION: State the application's broad, long-term objectives and specific aims, making reference to the health relatedness of the project. Describe conciseiy the research design and methods for achieving these goals. Avoid summaries of past accomplishments and the use of the first person. This abstract is meant to serve as a succinct and accurate description of the proposed work when separated from the application. If the application is funded, this description, as is, will become public information. Therefore, do not include proprietary/confidential information. DO NOT F._CEED THE SPACE PROVIDED. Human immunodeficiency virus type 1 (HIV-1) virions are released from cells as immature, noninfectious particles that must subsequently undergo proteolytic maturation to become infectious. Entry of virions into new target cells occurs through a membrane fusion reaction mediated by the Env glycoproteins gp120 and gp41. Although the mechanism of Env-catalyzed membrane fusion is relatively well characterized, less clear is the role of the 152 amino acid gp41 cytoplasmic domain in Env-mediated fusion. We have recently discovered that immature HIV-1 particles are inhibited for fusion through a mechanism involving the gp41 cytoplasmic tail (CT). Truncation of the tait_ or cleavage of Pr55Gag between the MA and NC domains, activates HIV-1 particles for fusion. This novel mechanism for regulating fusion may promote HIV-1 replication by enhancing productive entry of the virus, in addition, by inhibiting Env conformationat changes until the core has matured, the gp41-Gag interaction may confer a replicative advantage by limiting exposure of Env epitopes recognized by neutralizing antibodies. We propose here a series of six highly focused Specific Aims to dissect the mechanism of immature HIV-1 fusion inhibition and to determine the consequences to HIV-1 replication. Specifically, we will: 1. Determine whether maturation-dependent HIV-1 fusion extends to R5-tropic Env and Gag proteins from HIV-1 primary isolates; 2. Map the regions of the gp41 CT required for fusion inhibition; 3. Determine the role of lipid rafts in coupling HIV-1 fusion to virion maturation; 4. Quantify receptor-induced conformationat changes on immature HIV-1 particles; 5. Determine the role of viral RNA in fusion inhibition; and 6. Evaluate the role of the gp41 CT in conferring resistance to neutralizing antibodies during continuous HIV-1 replication. These studies will reveal new fundamental insights into the regulation of HIV-t entry and the role of the gp41 cytoplasmic tail in HIV-1 replication. PERFORMANCE SITE ========================================Section End===========================================
