       Document 0647
 DOCN  M9640647
 TI    The two biological activities of human immunodeficiency virus type 1 Vpu
       protein involve two separable structural domains.
 DT    9604
 AU    Schubert U; Bour S; Ferrer-Montiel AV; Montal M; Maldarell F; Strebel K;
       Laboratory of Molecular Microbiology, National Institute of; Allergy and
       Infectious Diseases, NIH, Bethesda, MD 20892-0460,; USA.
 SO    J Virol. 1996 Feb;70(2):809-19. Unique Identifier : AIDSLINE
       MED/96135190
 AB    The human immunodeficiency virus type 1 (HIV-1) Vpu protein is an
       integral membrane phosphoprotein that induces CD4 degradation in the
       endoplasmic reticulum and enhances virus release from the cell surface.
       CD4 degradation is specific, requires phosphorylation of Vpu, and
       involves the interaction between Vpu and the CD4 cytoplasmic domain. In
       contrast, regulation of virus release is less specific and not
       restricted to HIV-1 and may be mechanistically-distinct from CD4
       degradation. We show here that a mutant of Vpu, Vpu35, lacking most of
       its cytoplasmic domain has residual biological activity for virus
       release but is unable to induce CD4 degradation. This finding suggests
       that the N terminus of Vpu encoding the transmembrane (TM) anchor
       represents an active domain important for the regulation of virus
       release but not CD4 degradation. To better define the functions of Vpu's
       TM anchor and cytoplasmic domain, we designed a mutant, VpuRD,
       containing a scrambled TM sequence with a conserved amino acid
       composition and alpha-helical structure. The resulting protein was
       integrated normally into membranes, was able to form homo-oligomers, and
       exhibited expression levels, protein stability, and subcellular
       localization similar to those of wild-type Vpu. Moreover, VpuRD was
       capable of binding to CD4 and to induce CD4 degradation with wild-type
       efficiency, confirming proper membrane topology and indicating that the
       alteration of the Vpu TM domain did not interfere with this function of
       Vpu. However, VpuRD was unable to enhance the release of virus particles
       from infected or transfected cells, and virus encoding VpuRD had
       replication characteristics in T cells indistinguishable from those of a
       Vpu-deficient HIV-1 isolate. Mutation of the phosphorylation sites in
       VpuRD resulted in a protein which was unable to perform either function
       of Vpu. The results of our experiments suggest that the two biological
       activities of Vpu operate via two distinct molecular mechanisms and
       involve two different structural domains of the Vpu protein.
 DE    Amino Acid Sequence  Animal  Antigens, CD4/METABOLISM  Binding Sites
       Gene Products, vpu/CHEMISTRY/GENETICS/*METABOLISM  Hela Cells  Human
       HIV Seropositivity/BLOOD/IMMUNOLOGY  HIV-1/ISOLATION & PURIF/*METABOLISM
       Membrane Proteins/CHEMISTRY/GENETICS/METABOLISM  Molecular Sequence Data
       Mutagenesis, Site-Directed  Support, Non-U.S. Gov't  Support, U.S.
       Gov't, Non-P.H.S.  Support, U.S. Gov't, P.H.S.  Virion/METABOLISM
       JOURNAL ARTICLE

       SOURCE: National Library of Medicine.  NOTICE: This material may be
       protected by Copyright Law (Title 17, U.S.Code).

