Folding, assembly, and intracellular trafficking of the human immunodeficiency virus type 1 envelope glycoprotein analyzed with monoclonal antibodies recognizing maturational intermediates

Abstract

Monoclonal antibodies (MAbs) that bind linear or conformational epitopes on monomeric or oligomeric human immunodeficiency virus type 1 (HIV-1) envelope glycoproteins were screened for their recognition of maturational intermediates. On the basis of reactivities with gp160 at different times after pulse-labeling, the MAbs were sorted into groups that exhibited binding which was immediate and constant, immediate but transient, delayed, late, or very late. This grouping was consistent with the selectivity of the MAbs for structural features of gp160. Thus, a MAb to the V3 loop reacted with envelope proteins at all times, in accord with the relative conformational independence and accessibility of the epitope. Several MAbs that preferentially react with monomeric gp160 exhibited diminished binding after the pulse. A 10-min lag occurred before gp160 reacted with conformational MAbs that inhibited CD4 binding. The availability of epitopes for other conformational MAbs, including some that react equally with monomeric and oligomeric gp160 and some that react better with oligomeric forms, was half-maximal in 30 min and closely followed the kinetics of gp160 oligomerization. Remarkably, there was a 1-to 2-h delay before gp160 reacted with stringent oligomer-specific MAbs. After 4 h, approximately 20% of the gp160 was recognized by these MAbs. Epitopes recognized by monomerspecific or CD4-blocking MAbs but not by oligomer-dependent MAbs were present on gp160 molecules associated with the molecular chaperone BiP/GRP78. MAbs with a preference for monomers reacted with recombinant or HIV-1 envelope proteins in the endoplasmic reticulum, whereas the oligomer-specific MAbs recognized them in the Golgi complex. Additional information regarding gp160 maturation and intracellular trafficking was obtained by using brefeldin A, dithiothreitol, and a low temperature.

Rab11-FIP1C and Rab14 Direct Plasma Membrane Sorting and Particle Incorporation of the HIV-1 Envelope Glycoprotein Complex

“…Env is synthesized on ribosomes associated with the endoplasmic reticulum as a precursor protein, gp160 [5]. Trimerization of gp160 is required for exit from the ER [6]. During transit through the Golgi, gp160 becomes heavily glycosylated and the precursor subunits are cleaved by furin-like proteases to create gp41 (TM) and gp120 (SU) subunits.…”

Human immunodeficiency virus-1 Nef suppresses Hsp70-mediated Tat activation

“…Recent reports have found that heat shock proteins (HSPs) interact with viral particles. For instance, Hsp70 is associated with vesicular stomatitis [20], the vaccinia virus [21], adenovirus [22], and the gp160 glycoprotein of HIV (during its transportation and oligomerization) [23]. Nef interacts with Hsp40, resulting in an increase in Hsp40 translocation into the nucleus of the infected cells.…”

The C-terminal tail of the gp41 transmembrane envelope glycoprotein of HIV-1 clades A, B, C, and D may exist in two conformations: an analysis of sequence, structure, and function

“…Env mRNA is synthesized in the nucleus, and exported with the help of the viral Rev protein to the cytoplasm where it is translated as a gp160 precursor. Gp160 is then translocated through the rough endoplasmic reticulum (ER) (Dettenhofer and Yu, 2001), and folded with the assistance of the chaperone proteins, calreticulin, and calnexin (Otteken et al, 1996). Glycans are added in the Golgi, and subsequently trimmed (Dash et al, 1994;Fenouillet and Jones, 1995).…”