Profile of resistance of human immunodeficiency virus to mannose-specific plant lectins

Abstract

The mannose-specific plant lectins from the Amaryllidaceae family (e.g., Hippeastrum sp. hybrid and Galanthus nivalis) inhibit human immunodeficiency virus (HIV) infection of human lymphocytic cells in the higher nanogram per milliliter range and suppress syncytium formation between persistently HIV type 1 (HIV-1)-infected cells and uninfected CD4(+) T cells. These lectins inhibit virus entry. When exposed to escalating concentrations of G. nivalis and Hippeastrum sp. hybrid agglutinin, a variety of HIV-1(III(B)) strains were isolated after 20 to 40 subcultivations which showed a decreased sensitivity to the plant lectins. Several amino acid changes in the envelope glycoprotein gp120, but not in gp41, of the mutant virus isolates were observed. The vast majority of the amino acid changes occurred at the N glycosylation sites and at the S or T residues that are part of the N glycosylation motif. The degree of resistance to the plant lectins was invariably correlated with an increasing number of mutated glycosylation sites in gp120. The nature of these mutations was entirely different from that of mutations that are known to appear in HIV-1 gp120 under the pressure of other viral entry inhibitors such as dextran sulfate, bicyclams (i.e., AMD3100), and chicoric acid, which also explains the lack of cross-resistance of plant lectin-resistant viruses to any other HIV inhibitor including T-20 and the blue-green algae (cyanobacteria)-derived mannose-specific cyanovirin. The plant lectins represent a well-defined class of anti-HIV (microbicidal) drugs with a novel HIV drug resistance profile different from those of other existing anti-HIV drugs.

FIG. 1.

Schedule of drug-escalating selection of plant lectin (GNA [A] and HHA [B])-resistant HIV-1 strains as a function of time. Arrows indicate the time points when the virus isolates were made. Unbroken lines represent the subcultivation schedule in which supernatants were transferred with each passage, whereas broken lines represent the subcultivation schedule in which cell suspensions were transferred with each passage.

FIG. 2.

Alignment of the amino acids of HIV-1 gp120 according to Leonard et al. (22). Arrows represent amino acid mutations found in the plant lectin-resistant virus strains. Triangles represent glycosylation sites bearing high-mannose types of sugars. Squares represent glycosylation sites bearing complex types of sugars.

FIG. 3.

Core structure of gp120 according to the data of Kwong et al. (21). A ribbon diagram (left) and a topology diagram (right) are shown. The viral membranes are oriented above the core structure, and the target cell membrane is oriented below the core structure. The left portion of the core gp120 is indicated as the inner domain, the right portion is indicated as the outer domain, and the four-stranded sheet at the bottom left of gp120 is indicated as the bridging sheet. Loops are labeled LA to LF and V1 to V5. The five helixes are labeled α1 to α5. The 25 β-strands are shown as arrows. The approximate locations of the nine glycosylation sites that were mutated in the mutant virus strains are shown with asterisks.