Fig. 3.

Representative class averages of negatively stained α_vβ₈ and α_vβ₆ and their complexes with pro-TGF-β1. (A and B) The α_vβ₈ ectodomain (ecto) adopts an extended-closed conformation when either clasped (A) or unclasped (B). (C and D) The clasped and unclasped α_vβ₆ ectodomain exhibits both bent-closed and extended-closed conformations. The percentage of particles with each conformation is shown. (E–H) Clasped and unclasped α_vβ₈ ectodomain complexes with pro-TGF-β1 showed both 2:2 and 1:2 complexes. (I and J) The α_vβ₆ ectodomain 2:2 and 1:2 complexes with pro-TGF-β1. (K and L) The α_vβ₈ and α_vβ₆ headpieces adopt the closed conformation in the absence of bound ligand. (M and N) The 2:2 and 1:2 complexes of the α_vβ₈ headpiece and pro-TGF-β1. The headpiece remains closed. (O and P) The 2:2 and 1:2 complexes of the α_vβ₆ headpiece and pro-TGF-β1. Ligand binding induces headpiece opening. All samples were prepared in Mg²⁺/Ca²⁺, except the α_vβ₈ headpiece complex with pro-TGF-β1 was prepared in Mn²⁺/Ca²⁺. The α_vβ₆ class averages in I, J, L, O, and P were previously published (15, 18) and are shown for comparison. (Scale bar: 10 nm.)