HIV-1 Env glycoprotein is a trimer of heterodimeric gp120 and gp41 subunits that are produced from a gp160 precursor. The N terminus of gp160 contains a signal peptide (SP) which is essential for targeting the nascent protein to the endoplasmic reticulum where the Env SP is cleaved and removed from the maturing Env. Thus, the Env SP is not a part of the mature Env present on the surfaces of virions and infected cells. Nonetheless, similar to the mature Env, the Env SP displays an extraordinary genetic diversity, although its significance is not well understood. This study investigated the influence of SP sequence diversity on Env glycosylation and functions.
We constructed chimeric infectious molecular clones by swapping the native SPs of HIV-1 isolates CMU06 and SF162 with SPs from other HIV-1 isolates (MW965.26, 398F1, CH119, and 271.1). SP-swapped and WT viruses were produced in HEK293T and human peripheral blood mononuclear cells (PBMCs) and evaluated for site-specific glycan contents by mass spectrometry. We also assessed the effects of SP exchanges on DC-SIGN-mediated virus transmission and virus neutralization by monoclonal antibodies (mAbs).
Comparison of virion-derived total Envs from SP-swapped viruses vs their respective WT revealed strain-specific alterations in the proportions of oligomannose and complex glycans at many glycosites particularly at the trimer apex and base. Modified glycan compositions were associated with reduced DC-SIGN-mediated transmission of CMU06 but not SF162. Differential effects were also seen on CMU06 vs SF162 sensitivity to neutralization by mAbs targeting different epitopes, including V1V2, V3 and gp41.
These data demonstrate the contribution of SP in determining Env glycosylation, virus transmission and antibody recognition in a virus strain-specific manner. Hence, this study provides direct evidence for a critical role of the HIV Env SP in virus-host interaction.