Role of the intracytoplasmic tail of HIV-1 transmembrane glycoprotein in viral replication and cytopathicity

The role of HIV-1 envelope glycoprotein (Env) in virus replication and disease pathogenesis is being intensely explored due to cytopathic effects associated with Env expression. HIV-1 Env functions primarily as a fusogenic protein that mediates virus into target cells and also impacts cell-to-cell spread of the virus. While the determinants of receptor/coreceptor binding and membrane fusion are located on the ectodomain of the Env, the functions of the 150 amino acid intracytoplasmic segment remain largely undefined. Thus, in this dissertation, I focused on the functional significance of the intracytoplasmic tail of the HIV-1 Env in viral replication and cytopathicity. Based on the indispensable nature of the ICT in vivo and the presence of highly conserved structural motifs in the ICT referred to as lentivirus lytic peptides (LLP-1 and LLP-2), the principal hypothesis for the dissertation is that these LLP domains contribute to the structural and functional properties of Env, thereby impacting viral replication and cytopathicity. The overall experimental strategy has been to generate rationally designed point mutations in the LLP domains and evaluate the contributions of LLP-1 and LLP-2 domains in viral replication, envelope glycoprotein-mediated virus-cell and cell-cell fusion, Env structure and antigenicity, Env-induced cytopathicity, and T cell anergy.; Site-specific mutagenesis of the two LLP domains clearly demonstrated common functions of the LLP domains in cell-cell fusion. Interestingly, virus-cell fusion was unaffected by mutations in the LLP-2 domains, thereby rendering this mutant an important tool for understanding the mechanisms of envelope glycoprotein-mediated virus-cell and cell-cell fusion. However, despite structural similarity to LLP-2, only LLP-1 domain showed a distinct role in Env incorporation into virions. Via its effects on Env incorporation into virions, LLP-1 domain was found to impact the infectivity and replication of HIV-1 thereby presenting a potential target for therapeutic vaccines against HIV-1. Drugs targeting both LLP-1 and LLP-2 domains to abrogate cell-cell fusion also have significance in mitigating cell-cell spread of HIV-1 and virus-induced cytopathicity. Consistent with the conserved amphipathic α-helical properties of the LLP-2 domain, structural perturbations in this domain at the peptide level were found to translate into dramatic structural alterations in the ectodomain of both gp41 and gp120 as evidenced by altered antigenicity of the glycoprotein. (Abstract shortened by UMI.)...