ribbon_radius (float, default: 0.0) if greater than 0.0, controls the radius used when rendering the ribbon.
ribbon_sampling (integer, default: 1) controls how many segments are used between the guide points.
ribbon_side_chain_helper (boolean, default: off) controls whether or not atom and bond representations are automatically hidden for main chain atoms when the ribbon is shown.
ribbon_smooth (boolean, default: -1) controls whether or not the ribbon representation is drawn with smooth (antialiased) lines.