The map is of the membrane-spanning domain of
the nicotinic acetylcholine receptor in the closed
state, viewed from the synaptic cleft. The arrangement
of subunits around the central axis, clockwise beginning
from the bottom (closest to 0 on the y-axis) ia alpha,
gamma, beta, delta. The Fourier terms were derived
from tubular crystals having helical symmetry. They
are of higher quality along the meridional (y-axis)
direction than the equatorial direction (where the
diffraction is weaker and there is additional noise
associated with layer-line overlap. This has resulted in
some asymmetry in the map, with the best direction being
along the axis of the tube (y-axis). The map was obtained
by averaging data from four helical families in real
space, weighting each family approximately according
to the number of receptors analysed. The
actual weights were: 0.70 (-16,6); 0.30
(-15,7); 0.30 (-17,5); 0.25 (-18,6). As
explained in the Reference, the dominating low
resolution terms were weakened by
subtracting a map of the structure with terms
extending to only 15 Angstroms. THe weight
used for the subtraction map was -0.88.
The terms along the equator have also been
included with a weight of 0.04, so that
the densities corresponding to the
alpha-helical segments are represented at about
the same level throughout the thickness of the bilayer.
Suggested contour level:
2.18
Atlas images are either supplied by the depositor or generated by
EMDataBank using
UCSF Chimera.
