HIV-1 broadly neutralizing antibodies (bnAbs) target many viral variants, thereby holding promise for vaccine development. Antibodies bind to the HIV-1 spike protein, called “Env”, to prevent infectivity, but the virus evades immune responses through extensive Env glycosylation, mutation, and conformational heterogeneity. Interestingly, a class of HIV-1 bnAbs depends on the N332 glycan for binding and neutralization. Understanding how these antibodies develop and interact with Env will help guide vaccine design strategies to elicit similar antibodies in uninfected individuals. We previously determined an X-ray crystal structure of a synthetic Man9 glycopeptide, called “Man9-V3” in complex with a bnAb called DH270.6, produced in an HIV-1 infected individual designated CH848. Our superpositions with a more native Env showed that this glycopeptide mimics the variable loop 3 (V3 loop) of Env, suggesting that this glycopeptide could be useful for studying other antibody-glycan or antibody-Env interactions. Because HIV-1 bnAbs take years to develop and vaccination will likely require a prime-boost regimen, we are structurally and biochemically characterizing complexes with a glycan-dependent cooperating antibody, called DH475, also from patient CH848. This analysis will help us better understand events that lead to the initiation of the DH270.6 bnAb lineage. We crystallized DH475 in complex with Man9-V3 and with Man9 alone. Our structures show that the antibody binds solely to the glycan and not to the peptide, suggesting why DH475 is not broadly neutralizing. Docking studies suggest that DH475 could also contact a glycan on the Env V1-V2 loop. Such immune pressure could have led to the large deletions in this region of Env that were observed in the first year of infection. Moreover, co-elution studies of DH475 with Env fragments reveal that DH475 can only bind to monomeric, and not trimeric, Env. These data suggest that DH475 may bind to a non-functional form of the Env trimer, or a trimer that has shed. Additional studies between mutants will provide greater insights into how DH475 binds glycans and its significance in HIV-1 Env evolution in the CH848 patient.

Biochemical and structural analysis of an antibody-glycopeptide complex to understand initial events in antibody-HIV-1 co-evolution

ACS Spring Meeting 2021

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