The default ribbon path is a smooth bspline (semitransparent tan in the figure), which can diverge from the true positions of the backbone atoms (α-carbons shown as gray balls). A cardinal spline allows tracking the backbone more closely. Without smoothing (light blue), it follows the α-carbons exactly, or it can be combined with some “compromise” smoothing of strand and/or coil. Ribbon spline options can be set with the ribspline command or in the molecule model attributes.

Potassium channel (Protein Data Bank entry 1bl8) on a dark slate blue background with potassium ions shown in firebrick. The channel is comprised of four chains. Each chain has been rainbow-colored from blue at the N-terminus to red at the C-terminus, but only the surface of the channel is shown. The surface has been sliced with a per-model clipping plane. The surface cap color is plum except with opacity set to 0.8. The shininess and brightness have been set to 128 and 8, respectively, and the lights on the scene have been moved from their default positions. The subdivision quality (related to the smoothness of the spherical ions) is 5.0, and the molecular surface was computed with probe radius and vertex density set to 1.0 and 6.0, respectively. (More samples...)