1crn.pdb

This shows the backbone of a protein macromolecule by creating artificial 'backbone' bonds between alpha carbons. Backbone radius can be specified in angstroms.
  backbone
By default, the backbone bond color is inherited from the atoms (as with other bonds). You can explicitly change the backbone color.


This shows a spline trace of a protein backbone. The hermite spline curve passes through the mid-points between alpha carbon atoms
  trace
With color by 'structure' you get different colors for HELIX, TURN, and SHEET. Color by 'amino' and color by 'shapely' assign different colors to different amino acids.