Cartoon ribbons are drawn to pass through the exact positions of
peptide α-carbons in helix and coil, but by default,
strands are smoothed to appear less ripply. This means that α-carbons
in strands may not fall on the ribbon. A tether is drawn wherever a
sidechain is displayed but would otherwise be detached from the ribbon.
(Tether appearance can be adjusted with
cartoon
tether.)
However, β-strand ribbon smoothing can be tuned continuously between
zero (off) and 1.0 (default, fully on), and this can be done for all residues
or for specific residues only. The image compares ribbon positions for
residues 139 and 164 in the active site of mandelate racemase
(PDB 2mnr)
with and without smoothing.
The unsmoothed position (transparent blue) can be obtained with:
cartoon
:139,164 smooth 0
This leaves ribbon smoothing at other residues unchanged.
Values between 0 and 1 would give intermediate positions.
More features...