Missing loops not defined in the HIV-1-Env trimer crystal structure were modeled using Loopy63 (link). Missing side chains were modeled with Scap64 (link).
To model the N-linked glycan shield, we first determined all possible N-linked sequons in the HIV-1 Env trimer structure. A single asparagine residue in each sequon was targeted for computational N-linked glycan addition using a series of oligomannose 9 rotamer libraries at different resolutions. In constructing the rotamer libraries, the asparagine side chain rotamers were also considered. To avoid a combinatorial explosion in the search space, select torsion angles in the oligomannose 9 rotamer libraries were allowed to vary in increments between 30-60 degrees. We used an overlap factor (ofac) to screen for clashes between the sugar moieties and the trimer structure. The ofac between two nonbonded atoms is defined as the distance between two atoms divided by the sum of their van der Waal's radii. For the modeling carried out here, we set the ofac to a value of 0.60. For sterically occluded positions, the ofac was set to 0.55. To remove steric bumps between sugar moieties, all models were subjected to 100 cycles of conjugate gradient energy minimization using the GLYCAM65 (link) force field in Amber1266 with a distance-dependent dielectric.
To model the N-linked glycan shield, we first determined all possible N-linked sequons in the HIV-1 Env trimer structure. A single asparagine residue in each sequon was targeted for computational N-linked glycan addition using a series of oligomannose 9 rotamer libraries at different resolutions. In constructing the rotamer libraries, the asparagine side chain rotamers were also considered. To avoid a combinatorial explosion in the search space, select torsion angles in the oligomannose 9 rotamer libraries were allowed to vary in increments between 30-60 degrees. We used an overlap factor (ofac) to screen for clashes between the sugar moieties and the trimer structure. The ofac between two nonbonded atoms is defined as the distance between two atoms divided by the sum of their van der Waal's radii. For the modeling carried out here, we set the ofac to a value of 0.60. For sterically occluded positions, the ofac was set to 0.55. To remove steric bumps between sugar moieties, all models were subjected to 100 cycles of conjugate gradient energy minimization using the GLYCAM65 (link) force field in Amber1266 with a distance-dependent dielectric.
