10.1038/s41590-018-0235-7. site-wise glycan heterogeneity, have been Divalproex sodium determined for some isolates. While the extent of glycan shielding is usually conserved, the precise number, location, and processing of glycans, however, is strain dependent. New insights continue to reveal how such differences can impact bNAb activity and development. Novel approaches have exploited the glycan shield for designing immunogens that bind the germline precursors of bNAbs, a critical roadblock for vaccine-induction of bNAbs. Summary The HIV-1 glycan shield can significantly impact the induction and maturation of bNAbs, and a better understanding of how to manipulate it will improve immunogen design. strong class=”kwd-title” Keywords: Glycan shield, HIV-1 vaccines, broadly neutralizing antibodies Introduction The HIV-1 envelope glycoprotein (Env) is the most heavily glycosylated of viral glycoproteins [1]. Through their position and dynamics, glycans form a glycan shield that protects most of the Env surface Divalproex sodium against humoral responses, as glycans are recognized as self. The immense genetic diversity of HIV-1 world-wide requires successful Divalproex sodium vaccines to induce cross-reactive responses [2]. Thus, vaccines that can induce broadly neutralizing antibodies (bNAbs) with great cross-reactive potential are highly sought after. All known bNAbs have to negotiate the glycan shield, and the glycan shield properties of Env immunogens can dramatically alter antibody sensitivity [3*,4] and determine the targeted epitopes [5*]. Here, we PRKD2 review recent advances in our understanding of the HIV-1 glycan shield and its impact on bNAb interactions, as well as rational vaccine designs that exploit the Env glycan shield to induce bNAbs. Architecture and conservation of HIV-1 Env glycan shield. Envs of the global M-group strains have a median of 30 potential N-linked glycan sites (PNGSs) per protomer, with an inter-quartile range (IQR) of 28 to 31. These account for roughly half of the molecular weight of the Env glycoprotein. Glycans protrude out from the protein surface and are highly flexible, which provides a Divalproex sodium highly dynamic glycan shield [6,7*]. In addition, glycans are densely packed and form inter-glycan interactions, some of which can stabilize their dynamics [1,8*]. Until recently, glycan dynamics could not be directly observed, but were only accessible through molecular dynamics simulations. However, recent advances in cryoelectron microscopy (cryo-EM) now allow a direct, albeit low-resolution, visualization of the extent of glycan dynamics [9**]. We have developed a high throughput strategy of glycan shield mapping that accurately predicted glycan shield properties relevant for neutralizing antibody responses [5*]. Of the total number of Env glycans per protomer, a median of 7 (IQR=6C8) are distributed across the four hypervariable loops (typically 0C4 per hypervariable loop depending on the strain [4]). The hypervariable regions are largely unconstrained in their structure and exhibit immense sequence and length variation, even among viral quasispecies members in longitudinally followed individuals [10,11]. In fact, the length diversity precludes meaningful alignments both within and between infections, and thus, the precise placement of the glycan is usually strain-dependent. A Divalproex sodium median of 22 glycans (IQR = 21C24) are in regions outside the hypervariable loops (Fig. 1A). Amongst these, the majority are highly conserved, with 12 glycans present in greater than 90% and 19 glycans present in greater than 70% of M-group viruses (Fig. 1BCC). The remaining glycans are found at modest or low frequency. We previously have shown that a radius of 10? around each potential N-linked glycosylation site (PNGS) provides a good approximation of the impact of the glycan shield around the protein surface [5*]. Using this strategy, we mapped the glycan shield in ~4,500 M-group Envs, showing that despite the variation in PNGS locations, most of the outer regions of the Env trimer are shielded in the vast majority of M-group Envs (Fig. 1D). In particular, the region around the site 332 (oligomannose patch) contains PNGSs whose positions are variable among M-group Envs, and yet, this region is usually glycan.