Figure 3. Structure of Nup54-3·Nup58-2.
(A) The asymmetric unit consists of one Nup58-2 (red) protomer and two Nup54-3 protomers of different conformation (straight Nup54-3, green; bent Nup54-3, cyan). A symmetry-related unit is shown in gray and 2-fold axis of symmetry in black.
(B) Cartoon representation of the crystallographic hexamer, in which a heterotetramer consisting of two straight Nup54-3 conformers (green) and two Nup58-2 hairpins (red) forms a compact substructure. Nup54-3 caps are shown in gray.
(C) Structure of the crystallographic dodecamer. Three 2-fold axes of symmetry are indicated in black. Due to 2-fold symmetry, the dodecamer defines all interhexameric contacts.
(D) Residues that mediate hydrophobic (blue) and electrostatic (orange) interactions in the Nup54-3·Nup58-2 heterotetramer are shown in van der Waals sphere representation. The backbones of the heterotetramer (Nup58-2, red; straight Nup54-3, green) and bent Nup54-3 caps (gray) are indicated.
(E) Nature of the interactions between two Nup58-2·Nup54-3 heterotetramers and the two Nup54-3 clamps within the dodecamer. Interacting residues are indicated as in (D).