Figure 4.

Association of ASP with the plasma membrane and the viral envelope. Studies from our and other groups have shown that ASP is expressed on the surface of productively infected cells. In addition, our studies demonstrate that ASP co-localizes with gp120 on the surface of primary HIV-infected CD4+ T cells and macrophages. A putative model of membrane-associated ASP is shown on the left side of the figure. According to this model, the N-terminus and C-terminus of ASP are intracellular (or intraviral), while the segment between the two transmembrane domains is exposed in the extracellular (or extra-viral) milieu. This model is supported by evidence that our monoclonal antibody directed against an epitope in the predicted extracellular loop of the protein (residues highlighted in red) can detect ASP on the cell surface in flow cytometry and confocal microscopy studies without the need from membrane permeabilization [57]. The same monoclonal antibody could detect ASP on the surface of viral particles (fluorescence correlation spectroscopy), and could capture HIV-1 virions (virion capture assay) [57].