The “resolution revolution” in electron microscopy left some proteins behind: small helical bundles that are almost entirely membrane embedded. Decorating a target with recombinant antibody fragments (Fab) that bind in a structurally specific and rigid manner can overcome limitations of small particle alignment, but antibody discovery campaigns are expensive, time-consuming, and are not guaranteed to work. Here we identify a helical epitope from the HIV envelope protein (gp41) that can be engineered as a contiguous extension of the first transmembrane helix of diverse membrane proteins. We demonstrate the utility of this maneuver by complexing a single Fab to three unrelated, small membrane proteins. The strategy permitted us to crystallize an otherwise structurally-intractable 30-kDa fluoride channel, as well as visualize Fab fragment decoration by negative stain EM. This 17-amino acid a-helical epitope can be bound by distinct, structurally characterized Fab fragments that can aid in structure determination of the target membrane protein.