the angle between two helices

[Phil Xiang]

Re: the angle between two helices

There are several possible definitions of angles between two (interacting) 
helices:
1) The angle between the two vectors along the helical axes;
2) The dihedral angle defined by the two helical axes and a third line segment 
   formed by connecting the two points of contact on the two helices;
3) The dihedral angle defined by the two helical axes and a third line segment 
   formed by connecting the two centroids of the two helices;
Different definitions are suitable in different situations. For instance, when
measuring the angle between two transmembrane helices, definition 2 or 3 is more
meaningful than definition 1.


			
			Phil Xiang		
			Biophysics
			Brandeis University
			(617)736-4906