Characterization of a leucine-zipper-like domain in Vpr protein of human immunodeficiency virus type 1

Abstract

Human immunodeficiency virus type 1 (HIV-1) replicates productively in vitro in CD4 +-T cells and/or macrophages. In the host, however, HIV-1 replication may be restricted by the quiescence of susceptible cells. Vpr is a 15-kDa late viral gene product, which is assembled in the virion and suspected to enhance HIV-1 replication in the infected host. We demonstrated previously that Vpr interacted specifically with the cellular transcription factor Spl, and activated transcription from the HIV-1 long-terminalrepeat. Both Vpr-Spl interaction and trans-activation by Vpr required a central Leu/Ile-rich domain (LR domain, aa 60–81) in Vpr. This domain of Vpr was also found critical for Vpr interaction with another cellular protein of 180 kDa. We now provide biochemical evidence that the Vpr LR-domain has a leucine-zipper-like structure. The leucine-zipper structure has been found in a variety of cellular transcription factors, which use the leucine-zipper domain to form a specific dimer before they can bind to DNA through an upstream basic domain. The LR domain of HIV-1 Vpr, when fused to the basic domain of the cellular transcription factor CREB, was capable of supporting specific DNA binding by the CREB basic domain. Point mutational analysis of the Leu/Ile residues in the LR domain suggested that multiple Leu/Ile residues may be involved in maintaining the leucine-zipper-like structure. Mutagenesis in the context of the full-length Vpr also helped identify Leu/Ile residues critical for Vpr interaction with the cellular 180-kDa protein. These results suggested that the leucine-zipper-like domain may be an important functional determinant for HIV-1 Vpr.