Abstract: The present invention relates to the structure of Fab 4E10, e.g., as a complex with herein identified peptide KGND, herein identified as a 4E10 mimetope on gp41, as determined by crystallographic techniques, and the confirmation that peptide KGND has a functional relevant conformation, as well as the determination of key residues on 4E10, and uses thereof and compounds and compositions therefrom. Furthermore, the invention also relates to other peptides and mimetic peptides which bind to Fab 4E10.