A gp41 HR2 residue modulates the susceptibility of HIV-1 envelope glycoproteins to small molecule inhibitors targeting gp120

One characteristic of the HIV-1 CRF01_AE strain is that it contains a bulkier histidine residue at position 375 (H375) in its envelope glycoproteins (Env). This residue is part of the Phe43 cavity, where residue 43 of CD4 engages with gp120. It has been shown that H375 contributes to resistance against small molecule inhibitors targeting gp120. Residue 375 co-evolved with a few residues of the gp120 inner domain layers, and together they modulate the susceptibility of Env to small molecule gp120 inhibitors. Since residue 629 within the HR2 region of gp41 has also been proposed to have co-evolved with residue 375, we explored its role in the susceptibility of HIV-1 Env to two classes of small molecule gp120 inhibitors: the conformational blocker temsavir and the CD4-mimetic (CD4mc) BNM-III-170. Reversion of CRF01_AE isoleucine to a major clade methionine at position 629 had a significant but opposite impact on the susceptibility of the virus to temsavir and BNM-III-170. Mechanistically, this is associated with the capacity of residue 629 to modulate Env stability, as attested by its impact on cold inactivation. Overall, our results show how a single residue of HR2 contributes to the overall Env trimer stability and its susceptibility to gp120-targeted small molecule inhibitors.IMPORTANCECRF01_AE envelope glycoproteins (Env) have a well-conserved histidine at position 375. This residue is key in modulating the susceptibility of HIV-1 to small molecule Env inhibitors. Here, we report that a residue of the gp41 HR2 region affects Env trimer stability and its susceptibility to gp120-directed small molecule inhibitors. This work adds to our understanding of HIV-1 Env resistance to small molecule inhibitors.