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Figure 4.
A composite atomic model for the Y complex of the NPC,
emphasizing the role of the Nup84–Nup145C edge element as a
membrane curvature–stabilizing unit analogous to the
Sec31–Sec31 edge element in COPII vesicle coats. The long arm
of the Y complex is a composite model from crystal structures
and is shown with Nup145C in blue, Sec13 in orange, Nup84 in
green and Nup133 in yellow. The relative position of the
N-terminal propeller of Nup133 (yellow) and the short arm
components Nup120 (blue) and Nup85–Seh1 (blue–orange) are
more tentatively placed and shown half-transparent (see Results
for details). The long axis of the Y complex is oriented along
the positively curved nuclear envelope membrane, with the
concave face of the Nup84–Nup145C edge element facing the
lipid bilayer. This orientation is analogous to that of the
Sec31–Sec31 edge element in the COPII coat and is consistent
with the evolutionary relationship between the NPC and COPII
vesicle coat lattices. Notably, although the Y complex is shown
facing the membrane, it is not predicted to directly contact the
nuclear envelope. Rather, other nucleoporins are predicted to
have roles that correspond to adaptor complexes in other vesicle
coating systems that link the membrane curvature–stabilizing
coat (the Y complex) to the nuclear envelope.
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