Integrity of Glycosylation Processing of a Glycan-Depleted Trimeric HIV‑1 Immunogen Targeting Key B‑Cell Lineages

Broadly
neutralizing antibodies (bNAbs) that target the trimeric
HIV-1 envelope glycoprotein spike (Env) are tools that can guide the
design of recombinant Env proteins intended to engage the predicted
human germline precursors of bNAbs (gl-bNAbs). The protein components
of gl-bNAb epitopes are often masked by glycans, while mature bNAbs
can evolve to accommodate or bypass these shielding glycans. The design
of germline-targeting Env immunogens therefore includes the targeted
deletion of specific glycan sites. However, the processing of glycans
on Env trimers can be influenced by the density with which they are
packed together, a highly relevant point given the essential contributions
under-processed glycans make to multiple bNAb epitopes. We sought
to determine the impact of the removal of 15 potential N-glycan sites
(5 per protomer) from the germline-targeting soluble trimer, BG505
SOSIP.v4.1-GT1, using quantitative, site-specific N-glycan mass spectrometry
analysis. We find that, compared with SOSIP.664, there was little
overall change in the glycan profile but only subtle increases in
the extent of processing at sites immediately adjacent to where glycans
had been deleted. We conclude that multiple glycans can be deleted
from BG505 SOSIP trimers without perturbing the overall integrity
of the glycan shield.