Mutational Analysis of Conserved Domains within the Cytoplasmic Tail of gp41 from Human Immunodeficiency Virus Type 1: Effects on Glycoprotein Incorporation and Infectivity

Abstract

The transmembrane (TM) glycoprotein gp41 of human immunodeficiency virus type 1 possesses an unusually long (ϳ150 amino acids) and highly conserved cytoplasmic region. Previous studies in which this cytoplasmic tail had been deleted partially or entirely have suggested that it is important for virus infectivity and incorporation of the gp120-gp41 glycoprotein complex into virions. To determine which regions of the conserved C-terminal domains are important for glycoprotein incorporation and infectivity, several small deletions and amino acid substitutions which modify highly conserved motifs were constructed in the infectious proviral background of NL4.3. The effects of these mutations on infectivity and glycoprotein incorporation into virions produced from transfected 293-T cells and infected H9 and CEM؋174 cells were determined. With the exception of a mutation deleting amino acids QGL, all of the constructs resulted in decreased infectivity of the progeny virus both in a single-round infectivity assay and in a multiple-infection assay in H9 and CEM؋174 cells. For most mutations, the decreased infectivity was correlated with a decreased incorporation of glycoprotein into virions. Substitution of the arginines (residues 839 and 846) with glutamates also reduced infectivity, but without a noticeable decrease in the amount of glycoprotein incorporated into virus produced from infected T cells. These results demonstrate that minor alterations in the conserved C-terminal region of the gp41 cytoplasmic tail can result in reductions in infectivity that correlate for most but not all constructs with a decrease in glycoprotein incorporation. Observed cell-dependent differences suggest the involvement of cellular factors in regulating glycoprotein incorporation and infectivity.

The Membrane-Proximal External Region of the Human Immunodeficiency Virus Type 1 Envelope: Dominant Site of Antibody Neutralization and Target for Vaccine Design

“…Mutagenesis studies of CT suggest that it is involved in Env incorporation into the virus (184,260), decreased virus infectivity (251), and structural perturbations of gp120 leading to increased sensitivity to Ab-mediated neutralization (67). Other functions have been described for CT, including interaction with the viral matrix protein (48,62,72,160,260), targeting to vesicles (56,129,194), as well as interaction with other proteins (15, 102, 152, 171, 252).…”

Altered Interaction of the Matrix Protein with the Cytoplasmic Tail of Hemagglutinin Modulates Measles Virus Growth by Affecting Virus Assembly and Cell-Cell Fusion

“…It is also suggested that the cytoplasmic tails of envelope proteins or their interactions with M proteins are important for the efficient assembly of paramyxoviruses (6,8,9,40,41,51,52,55), rhabdoviruses (41,56), orthomyxoviruses (18,24,41), and retroviruses (17,34). Interestingly, using the Edmonston vaccine strain, Naim et al showed that the MV M protein controls the sorting of the H and F proteins (26).…”

Truncation of the Cytoplasmic Domain Induces Exposure of Conserved Regions in the Ectodomain of Human Immunodeficiency Virus Type 1 Envelope Protein

“…A peculiar feature of gp41 is its unusually long cytoplasmic domain, typically about 150 amino acids. Truncation of the cytoplasmic domain in vitro has been associated with enhanced fusion activity but with reduced viral infectivity (19,35,36,40). In vitro passage of SIVmac in certain human cell types has been shown to select for variants with truncated cytoplasmic domains, although the nature of the resulting growth advantage remains unclear (27).…”