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Background:  HIV and other retroviruses exit infected cells by budding from the plasma membrane. Viral budding and viral releases require interactions between the HIV-1 Gag protein p6 and the cellular host proteins TSG101 and AIP1, which are mediated by short and highly conserved specific amino acid motifs in p6gag (PT/SAP, LYP, LRSL). We examined the variability of those p6gag domains in distinct HIV-1 subtypes and under the influence of antiretroviral therapy.

Methods:  PT/SAP, LRSL, and LYP sequences within p6gag were analyzed in specimens belonging to different clades (A, B, C, F, G, H, and J) and collected from 123 HIV-infected individuals. Sixty-eight subjects carried gag non-B sequences (49A, 2C, 1F, 13G, 1H, 1J, 1U). One-third of the sample was under ARV therapy, including protease inhibitors.

Results:  HIV-1 subtype influenced the variability at Gag motifs involved at viral budding. The rate of amino acid insertions at the PT/SAP motif and substitutions at the LRSL domain differed when considering B and non-B viruses, regardless the presence of ARV therapy. In more detail, 33% of subjects carrying clade B viruses presented insertions at the p6gag protein, while it was seen in only 6% of individuals infected with non-B viruses (p = 0.0001). Most (up to 70%) were located nearby the PT/SAP motif. Those insertions (from 3 to 9 residues) included duplications or partial duplications of the PT/SAP motif, effectively lengthening the TSG101 binding site. A higher percentage of non-B than B viruses presented the change R42K within the LRSL motif (90% vs  49%, p < 0.0001). Antiretroviral therapy decreased the percentage of subjects carrying mutations in the LYP budding-related p6gag motif (from 42% to 14%; p = 0.02), but only in subtype B viruses. However, antiretroviral therapy did not alter the variability on PT/SAP and LRSL domains.

Conclusion: Amino acid sequences in viral domains involved in the interaction with host cell proteins necessary for HIV budding may vary according to HIV subtype as well as under antiretroviral pressure. The effect of gag variability on budding in different HIV-1 clades needs to be further studied.

Keywords: gag; HIV-1 Subtypes; budding