The glycan shield of the HIV-1 envelope glycoprotein complex (Env), in particular the glycan at position 332 in gp120, is frequently targeted by broadly neutralizing antibodies (bNAbs) isolated from HIV-1 infected individuals. We investigated the role of the second amino acid position of the N332 glycosylation motif Asn-X-Ser in HIV-1 evolution and neutralization sensitivity.
DESIGN AND METHODS
The neutralization sensitivity of viral variants harbouring glycosylation motifs with different probabilities of glycan occupancy were tested for a subset of N332-dependent bNAbs. Furthermore, longitudinal Env sequences of 37 HIV-1 infected individuals were used to analyse the evolution of the N332 glycosylation motif within these individuals. Finally, early Env sequences from 31 historical and 21 contemporaneous seroconverters were compared to analyse this evolution on a population level.
Viral variants with a higher probability of N332 occupancy were more sensitive for neutralization by some N332-dependent bNAbs. Furthermore, the longitudinal analyses revealed an increase in probability of glycan occupancy of the N332 site over time, both within patients, and at the population level over the course of 20 years of HIV-1 epidemic.
These observations suggest that modulation of N332 glycan occupancy by the second amino acid position of the canonical glycosylation motif Asn-X-Ser plays a previously unappreciated role in viral escape from immune responses, and should be considered in Env-based vaccine design.