Table 1

Phenotypes of HIV-1 YU2 gp120 mutants. The ability of the wtΔ and mutant glycoproteins to bind CCR5 expressed on L1.2 cells was determined (10). The recognition of the wtΔ and mutant glycoproteins by sCD4 and monoclonal antibodies that recognize discontinuous gp120 epitopes (5, 14) was determined (10). All values reported are relative to those seen for the wtΔ protein. Values represent the average of at least two independent experiments and exhibit less than 30% variation from the value shown.

Protein (FSA)*CCR5 bindingLigand binding
107 D/R1.021.020.971.111.14
114 Q/L1.220.790.730.710.75
117 K/D (0.45)0.150.740.640.420.83
121 K/D (0.57)0.070.730.11§ 0.00.99
122 L/S0.980.841.070.181.11
123 T/D (0.49)0.080.99§
197 N/D1.331.340.800.811.11
199 S/L1.501.320.941.031.04
200 V/S0.840.911.05§ 0.491.06
201 I/A0.460.900.670.840.81
203 Q/L0.680.850.88§ 0.520.93
207 K/D (0.23)0.00.850.460.130.98
209 S/L1.001.110.851.011.00
210 F/S0.650.810.810.850.74
211 E/K0.731.
257 T/D0.050.0§ 0.490.060.0
295 N/E0.860.750.730.980.79
308 N/D0.311.100.890.931.03
317 L/S0.
330 H/A0.220.750.550.660.64
ΔV3 (Δ298-329)0.00.800.081.270.93
370 E/Q0.170.0§
372 V/S0.851.
373 T/D0.481.
377 N/E (0.04)0.220.710.520.650.60
381 E/R (0.07)0.070.810.750.290.96
383 F/S0.
386 N/D1.221.140.970.900.97
419 R/D (0.82)0.190.860.02§ 0.480.82
420 I/R (0.14)0.060.590.0§ 0.720.72
421 K/D (0.32)0.070.860.19§ 0.00.0
422 Q/L (0.35)0.070.530.0§ 0.200.55
423 I/S0.610.970.05§ 0.301.03
424 I/S0.370.250.480.830.81
426 M/A0.750.69§ 0.690.721.11
429 E/R1.541.17§
432 K/A0.611.00.92§ 0.01.45
434 M/A1.220.900.65§ 0.071.04
435 Y/S0.210.330.22§ 0.291.00
436 A/S0.981.050.910.991.23
437 P/A1.790.800.68§ 0.780.82
438 P/A (0.28)
439 I/A0.450.680.760.760.84
440 R/D (0.43)
441 G/V (0.91)0.00.670.700.620.78
442 Q/L2.001.110.741.050.83
444 R/D (0.80)0.250.790.670.940.74
474 D/R1.030.59§ 0.810.740.0
  • * The residue number of the mutant wtΔ glycoproteins is based on the sequence of the prototypic HXBc2 gp120 glycoprotein (27), with 1 representing the initiator methionine. The wild-type YU2 gp120 residue is listed first, followed by the substituted residue (25). The fractional solvent accessibilities (FSAs) associated with gp120 residues in which changes specifically disrupted CCR5 binding are shown in parentheses. Fractional solvent accessibility was calculated as the ratio of solvent-accessible surface area for atoms of amino acid residue X in the gp120 core (without carbohydrate moieties) to the area obtained after reduction of the structure to a Gly-X-Gly tripeptide (24). Values cited are for side-chain atoms, except for glycine-441 where the value for all atoms is given.

  • The binding of the wtΔ glycoprotein to L1.2-CCR5 cells was shown to be linearly related to the concentration of wtΔ protein in the transfected 293T cell supernatants, over the range of concentrations used in these experiments (13). The total amount of wtΔ and mutant glycoprotein present in the 293T cell supernatants was estimated by precipitation with an excess of a mixture of sera from HIV-1–infected individuals. The amount of wtΔ and mutant glycoprotein bound to the L1.2-CCR5 cells was determined as described (10). The value for CCR5 binding was calculated with the following formula: CCR5 binding = (Bound mutant protein ÷ Bound wtΔ protein) × (Total wtΔ protein ÷ Total mutant protein).

  • The recognition of the wtΔ and mutant glycoproteins by sCD4 and antibodies was determined by precipitation of radioactively labeled envelope glycoproteins in transfected 293T cell supernatants as described (10). In parallel, the labeled envelope glycoproteins were precipitated with an excess of a mixture of sera from HIV-1–infected individuals. The value for ligand binding was calculated with the following formula: Ligand binding = (Mutant proteinligand ÷ wtΔ proteinligand) × (wtΔ proteinserum mixture ÷ Mutant proteinserum mixture).

  • § In the sCD4 and 17b columns, the values indicate gp120 residues that exhibit decreased solvent accessibility in the presence of the two-domain sCD4 or 17b Fab, respectively, in the ternary complex (6). Changes in solvent accessibility were calculated with the MS program of M. Connolly (26).