Hi Francesco,

On Apr 19, 2010, at 12:29 AM, Francesco Pietra wrote:

If at all, I did not understand if a continuous trace of the centroid
(instead of a series of balls) can be obtained in the context of the
protein. That would improve the presentation further. Otherwise, the
series of balls for the centroid, with appropriate choice of radius
and step size, shows the pathway of the ligand through the protein
adequately.

Nothing simple comes to mind.  One way that's a bit of work would be to save the centroid information to a file (the 'Save' button on the Axes/Planes/Centroids interface) and the use a text editor to create a BILD file (BILD format) showing lines/cylinders connecting the centroid centers.

As a minor point, I was unable to render helices transparent.
Transparency would help to to see the centroid trajectory in between
helices.

Should be possible unless there's something wrong with your graphics cards.  Try this:

Select->Structure->secondary structure->helix
Actions->Color->from editor

This will bring up a color editor.  Try making a transparent red.  For me, the editor looks like this when I do that:

(note the "Opacity" box is checked)

and the structure looks like this:


--Eric


                        Eric Pettersen

                        UCSF Computer Graphics Lab

                        http://www.cgl.ucsf.edu