FIG. 4.
H stalk residues 111, 114, and 118 are determinants for physical and functional interaction of MeV H and F. F-Edm, MeV Edmonston F. (A) Characterization of H variants harboring individual alanine point mutations as in Fig. 2A. Values represent the averages from at least three independent experiments ± SEMs. Only mutation of residue 111, 114, or 118 substantially reduces F triggering activity. (B) In an α-helical configuration of the H stalk, residues 111, 114, and 118 are predicted to be located adjacent to each other on consecutive turns of the helix. Solvent-accessible surface models of H stalk dimers cover positions 103 to 125. Side chains of residues 111, 114, and 118 are shown in dark gray, and side chains of residues 108 and 122 are shown in light gray. The translucent surface with a ribbon trace (left panel) reveals a possible helix break at P108, making residue 111 accessible (orientation toward the viewer). The opaque surface (right panel) reveals that side chains of residues 111, 114, and 118 form a continuous patch. (C) Co-IP of surface-exposed, matured MeV F with MeV H after DTSSP cross-linking as in Fig. 2E. Values represent averages from four independent experiments ± SEMs. H-ER retained, an H variant carrying a cytosolic endoplasmic reticulum retention motif; IP, immunoprecipitation; αH and αF, antibodies to H and F, respectively.