Expression and biochemical analysis of the entire HIV‐2 gp41 ectodomain: determinants of stability map to N‐ and C‐terminal sequences outside the 6‐helix bundle core

The folding of HIV gp41 into a 6‐helix bundle drives virus‐cell membrane fusion. To examine the structural relationship between the 6‐helix bundle core domain and other regions of gp41, we expressed in Escherichia coli , the entire ectodomain of HIV‐2 ST gp41 as a soluble, trimeric maltose‐binding protein (MBP)/gp41 chimera. Limiting proteolysis indicated that the Cys‐591–Cys‐597 disulfide‐bonded region is outside a core domain comprising two peptides, Thr‐529–Trp‐589 and Val‐604–Ser‐666. A biochemical examination of MBP/gp41 chimeras encompassing these core peptides indicated that the N‐terminal polar segment, 521–528, and C‐terminal membrane‐proximal segment, 658–666, cooperate in stabilizing the ectodomain. A functional interaction between sequences outside the gp41 core may contribute energy to membrane fusion.