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Figure 7.
FIGURE 7. Assessment of contiguous helicity by secondary
chemical shifts and dihedral angle order parameter. A, ^1H
secondary chemical shifts for TM IX in DPC micelles. ^1H
chemical shifts assignments from homonuclear two-dimensional
NOESY (225-ms mixing time) and two-dimensional TOCSY spectra
collected on an 800-MHz spectrometer. Random coil shifts (59)
were subtracted from the empirical values, and the resulting
secondary chemical shifts are shown for H^  . The solid line is the
chemical shift difference cutoff considered significant (for
helicity) for the ^1H chemical shift index (60). B,  and  backbone
dihedral angle order parameter for each residue of the TM IX
peptide. (dashed line) and (solid
line) dihedral angle order parameters were calculated as
described previously (61). Briefly, if the dihedral angle has
the same value in all 40 structures of the retained NMR
ensemble, its order parameter will be 1. An order parameter of 0
represents a completely random dihedral angle across the
ensemble, and values 0 < order parameter < 1 represent variable
dihedral angles. This parameter is used in place of the
alternative measure of angular standard deviation, which does
not have a defined value for truly random angles.
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