Figure 3.
Fig. 3. (A) Comparison of the homologous membrane-spanning
subunits HI1471 and BtuC, after superposition of TM2 in subunit
A (to the left) of each structure, as viewed down the molecular
two-fold axis from the periplasm. With the exceptions of TM3 to
TM5, the helices in the A subunits of HI1471 (cyan) and BtuC
(purple) superimpose closely. In contrast, interconversion of
the B subunits (to the right) between these two structures (blue
and red, respectively) requires an 9° twist
(indicated by the curved arrow) about an axis oriented in the
direction shown to the right, which passes through the helical
domain of the ABC subunit. (B) Stereoview of a superposition of
helices TM3, TM4, TM5, TM8, TM10, and 5a in subunit A of HI1471
(cyan) and BtuC (purple), as viewed from within the permeation
pathway with the molecular two-fold axis vertical. The internal
symmetry–relating helices TM3 and TM8 and TM5 and TM10, as
well as the irregular structures of TM3 and TM8, may be
observed. The extramembrane helix 5a helps restrict the
permeation pathway on the periplasmic side of HI1470/1.
The above figure is reprinted
by permission from the AAAs:
Science
(2007,
315,
373-377)
copyright 2007.
9° twist
(indicated by the curved arrow) about an axis oriented in the
direction shown to the right, which passes through the helical
domain of the ABC subunit. (B) Stereoview of a superposition of
helices TM3, TM4, TM5, TM8, TM10, and 5a in subunit A of HI1471
(cyan) and BtuC (purple), as viewed from within the permeation
pathway with the molecular two-fold axis vertical. The internal
symmetry–relating helices TM3 and TM8 and TM5 and TM10, as
well as the irregular structures of TM3 and TM8, may be
observed. The extramembrane helix 5a helps restrict the
permeation pathway on the periplasmic side of HI1470/1.