The human being immunodeficiency virus type 1 (HIV-1) envelope glycoprotein trimer consists of gp120 and gp41 subunits and undergoes a series of conformational changes upon binding to the receptors CD4 and CCR5/CXCR4 that promote virus entry. change H66N in the gp120 exterior envelope glycoprotein. Histidine 66 is located within the gp41-interactive inner domain of gp120 and in other studies has been shown to decrease the sampling of the CD4-bound conformation by unliganded gp120. Substituting asparagine or other amino acid residues for histidine 66 in cold-sensitive HIV-1 envelope glycoproteins resulted in cold-stable phenotypes. Cold inactivation of the HIV-1 envelope glycoproteins occurred even at high pH indicating that protonation of histidine 66 is not necessary for this process. Increased exposure of epitopes in the ectodomain of the gp41 transmembrane envelope glycoprotein accompanied cold inactivation but shedding of gp120 did not. An amino acid change in gp120 (S375W) that promotes the CD4-bound condition or treatment with soluble Compact disc4 or a small-molecule Compact disc4 mimic led to increased cool sensitivity. These total results indicate how the CD4-bound intermediate from the HIV-1 envelope glycoproteins is cool labile; avoiding the Compact disc4-bound state raises temperature stability. Human being immunodeficiency pathogen type 1 (HIV-1) can be an enveloped pathogen that like all retroviruses consists of ABT-869 two copies of genomic RNA and several enzymes required for viral replication (5). One of these enzymes reverse transcriptase (RT) converts the viral RNA into DNA in the cytoplasm of the newly infected cell (4 66 HIV-1 entry into target cells is usually mediated by the viral envelope glycoproteins which are assembled into a trimeric complex around the virion surface (39 48 Previous studies identified RT and the envelope glycoproteins as the HIV-1 components most vulnerable to inactivation by high temperature (38). In infected virus-producing cells the HIV-1 envelope glycoproteins are synthesized as an approximately 860-amino-acid precursor. This precursor is usually extensively glycosylated to produce the gp160 envelope glycoprotein which assembles into trimeric complexes. Proteolytic cleavage of gp160 creates the gp120 exterior envelope glycoprotein and the gp41 transmembrane envelope glycoprotein. The three gp120 envelope glycoproteins in the trimeric complex associate noncovalently with the gp41 envelope glycoproteins which are anchored in the membrane. Following the conversion of a subset of the glycan residues to complex carbohydrates the trimeric envelope glycoprotein complex is ABT-869 usually transported to the cell surface from which it may be incorporated into the membranes of budding virions (3 8 9 20 43 70 HIV-1 entry involves the viral envelope glycoproteins and receptors on the target cell surface. The receptor CD4 and chemokine receptor CCR5 or CXCR4 are recognized by gp120 (11-13 15 19 33 Receptor binding triggers conformational changes in the envelope glycoprotein complex that eventually promote the fusion of the viral and target cell membranes a process that is usually essential for virus entry and that is mediated by the gp41 transmembrane glycoproteins. In this manner the high potential energy of the unliganded HIV-1 envelope glycoprotein complex is usually channeled via ABT-869 multiple metastable intermediate says into the force required to ABT-869 fuse the membranes of virus and target cell (16 44 71 73 Under some circumstances the HIV-1 envelope glycoprotein complex undergoes inactivating conformational changes. For example soluble forms of the CD4 receptor (sCD4) in addition to competing for target cell CD4 can also trigger conformational changes in the HIV-1 envelope glycoproteins that lead to functional inactivation (H. Haim submitted for publication). In the extreme ABT-869 sCD4 binding causes the shedding of the gp120 glycoprotein from the envelope glycoprotein complex (23 28 45 The efficiency of gp120 shedding Rabbit polyclonal to GLUT1. is much greater at 37°C than at room temperature (47 52 The inactivation of the HIV-1 envelope glycoproteins in the absence of sCD4 is much slower than after sCD4 incubation (H. Haim submitted). Here we subjected a molecularly cloned HIV-1 to repeated rounds of selection at elevated temperatures. As expected the selected virus was more stable than the parental virus at high temperatures. Surprisingly the parental virus was inactivated on ice more rapidly than at room temperature; the heat-selected virus was resistant to this cold inactivation. Unlike heat inactivation which involves multiple components of the virus (38) sensitivity to the cold was determined solely by.