Levels of N-linked glycosylation on the V1 loop of HIV-1 Env proteins and their relationship to the antigenicity of Env from primary viral isolates

A good understanding about the structure and function of the envelope glycoprotein (Env) from primary human immunodeficiency virus-1 (HIV-1) isolates is important in facilitating the development of effective neutralizing antibody responses as a component of an effective HIV-1 vaccine. In the current study, the antigenicity of a panel of diverse HIV-1 primary Env from different clades of HIV-1 Group M was analyzed using rabbit sera produced by either 3- or 9-valent gp120 DNA vaccine formulations. Both the 3- and 9-valent gp120 DNA vaccine formulations elicited HIV-1 gp120-specific antibodies in immunized rabbits. However, we observed two levels of primary envelope antigenicity to the same set of rabbit immune sera and that the level of glycosylation, particularly in the V1 loop, may contribute to such diversity. Bioinformatics analysis on the distribution and average number of the N-linked glycosylation sites in all variable regions (V1-V5) was conducted. A linear plot demonstrated that the average number of potential N-glycosylation sites in the V1 and V4 loops correlates to the size of the loop. These data provide further evidence on the complexity of primary HIV-1 Env antigens and offers new insight into the mechanisms that HIV-1 uses to escape protective immune responses.