Protein backbone

This is crambin (1crn.pdb).

Backbone

Shows the folding of the polypeptide chain by creating artificial 'backbone' bonds between alpha carbons. Backbone thickness can be specified as radius in angstroms.
  backbone

By default, the backbone color is inherited from the reference atoms, i.e. carbon gray. You can explicitly change the color:

Trace

Alternatively, a smooth curve may be used to display the 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.