Phenotypes of SIVmac239 gp120 mutantsa

Mutation(s)bResidue locationAssociation indexcProcessing indexdRelative infectivityeCell-to-cell fusionfCD4-Ig bindingg
V36AN terminus0.260.980.461.291.88
Y40AN terminus0.811.200.480.761.30
N47AN terminus1.050.560.261.250.53
L52ALayer 10.410.700.040.970.54
T56ALayer 10.380.720.100.880.73
R61ALayer 10.280.820.230.671.03
R61SLayer 10.360.93<
D62ALayer 10.120.49<0.010.881.17
W69LLayer 10.340.580.020.890.96
W69FLayer 10.230.840.011.021.38
T72ALayer 10.380.800.111.140.83
Q73ALayer 10.270.670.031.090.82
P76ALayer 10.940.81<
N78ALayer 10.960.890.010.080.67
G79SLayer 11.190.850.470.910.61
Q103ALayer 20.170.78<0.010.940.01
D107ALayer 20.480.880.010.870.46
W109ILayer 20.960.950.450.530.85
L111ALayer 20.560.830.070.850.49
F112ALayer 20.070.750.011.170.23
F215ALayer 20.250.14<0.010.640.01
R216ALayer 20.620.300.020.010.23
Y217ALayer 20.580.100.010.47NA
P221ALayer 20.420.570.060.180.46
W375SPhe 43 cavity0.761.090.240.410.48
K487AC terminus0.340.080.031.07NA
V491AC terminus0.370.260.441.280.22
I494AC terminus0.070.370.010.841.88
L496AC terminus0.140.590.281.171.52
W69L/W375SLayer 1/Phe 430.321.360.020.780.27
D107A/W375SLayer 2/Phe 430.441.470.030.970.37
W109I/W375SLayer 2/Phe 430.651.
L111A/W375SLayer 2/Phe 430.871.580.030.580.27
  • a Values presented in this table represent the means of data from at least two independent experiments, with experimental variation typically not more than 20% of the value reported.

  • b The numbering of the SIVmac239 gp120 envelope glycoprotein amino acid residues is based on that of the prototypic HXBc2 strain of HIV-1, where 1 is the initial methionine (37). The mutations result in the substitution of the amino acid residue shown on the right for the amino acid residue shown on the left of the number; for example, W69L indicates a substitution of a leucine residue for the tryptophan residue at position 69.

  • c The association index is a measure of the ability of the mutant gp120 molecule to remain associated with the envelope glycoprotein complex on the expressing cell relative to that of the wild-type envelope glycoproteins. The association index is calculated as follows: association index = ([mutant gp120]cell × [wild-type gp120]supernatant)/([mutant gp120]supernatant × [wild-type gp120]cell).

  • d The processing index is a measure of the conversion of the mutant gp160 envelope glycoprotein precursor to mature gp120 relative to that of the wild-type envelope glycoproteins. The processing index was calculated by the following formula: processing index = ([total gp120]mutant × [gp160]wild-type)/([gp160]mutant × [total gp120]wild-type).

  • e Relative infectivity was assessed by infecting Cf2Th-CD4/CCR5 cells with similar amounts of recombinant HIV-1 pseudotyped with wild-type and mutant SIVmac239 envelope glycoproteins, normalized according to reverse transcriptase (see Materials and Methods). The ratio of mutant/wild-type virus infectivity is reported.

  • f Cell-cell fusion ability was assessed by coincubation for 6 h at 37°C of 293T cells expressing the SIVmac239 envelope glycoprotein variants with the reporter TZM-bl cells, as described in Materials and Methods. ND, not determined.

  • g Normalized amounts of radiolabeled wild-type and mutant gp120 glycoproteins were incubated with 13 nM CD4-Ig for 1 h at 37°C. The immunoprecipitates were washed, run on SDS-polyacrylamide gels, and analyzed by densitometry. NA, not applicable, because the levels of gp120 secreted into the supernatant for these mutants were not sufficient to assess CD4 binding.