Large HIV gp41 construct with final trimer-of-hairpins structure exhibits V2E mutation-dominant attenuation of vesicle fusion and helicity that is quantitatively similar to V2E attenuation of HIV fusion and infection and supports: (1) hairpin stabilization of initial membrane apposition with larger apposition distance for V2E; and (2) V2E dominance mediated by an antiparallel β sheet with interleaved fusion peptide strands from two gp41 trimers