Figure 4.
Figure 4. Various crystalline oligomers of Pae and Mth
SmAP1. A unit cell of the Pae SmAP1 C222[1] crystal form is
shown in (A), along with examples of crystallographic twofold
and 2[1] screw axes. The asymmetric unit is a heptamer (shown as
C traces in red
or blue), and a Pae SmAP1 14-mer with 72-point group symmetry is
formed from adjacent asymmetric units (7550 Å2 of surface area
is buried at the heptamer-heptamer interface). Orthogonal views
of the quasihexagonal packing of Mth SmAP1 heptamers in the
P2[1]2[1]2[1] crystal form are shown in (B). Heptamers stack
upon one another to form cylindrical tubes, thus providing a
model for the structure of the EM fibrils (see text for
explanation). The head-to-tail association of heptamers gives
the tubes a defined polarity (colored arrows). Molecular
surfaces show that the lateral packing of tubes in the crystal
may generate the striated bundles seen by EM.
traces in red
or blue), and a Pae SmAP1 14-mer with 72-point group symmetry is
formed from adjacent asymmetric units (7550 Å2 of surface area
is buried at the heptamer-heptamer interface). Orthogonal views
of the quasihexagonal packing of Mth SmAP1 heptamers in the
P2[1]2[1]2[1] crystal form are shown in (B). Heptamers stack
upon one another to form cylindrical tubes, thus providing a
model for the structure of the EM fibrils (see text for
explanation). The head-to-tail association of heptamers gives
the tubes a defined polarity (colored arrows). Molecular
surfaces show that the lateral packing of tubes in the crystal
may generate the striated bundles seen by EM.