Modevectors

Example showing modevectors in action. (See Examples below).

DESCRIPTION

modevectors.py is a PyMol script that was originally written to visualize results obtained from Normal Mode Analysis (NMA) by drawing arrows or vectors from a starting structure to a final structure. However, this script can be used to visualize the direction of motion between two specified states (e.g. targeted MD, comparing open and closed structures, etc). The strength of this script is that the arrows are highly customizable with numerous options to choose from (see script below). It is important to note that the two states MUST be identical except for the X, Y, and Z coordinates. That is, you cannot draw vectors between homologous structures. The default settings sets the background to white and displays the arrows along with the first object frame (in cartoon representation).

USAGE

load the script using the run command

modevectors first_obj_frame, last_obj_frame [,outname=modevectors [,head=1.0 [,tail=0.3 \
  [,head_length=1.5 [,headrgb=(1.0,1.0,1.0) [,tailrgb=(1.0,1.0,1.0) [,cutoff=4.0 [,skip=0 \
  [,cut=0.5 [,atom=CA [,stat=show [,factor=1.0]]]]]]]]]]]

Please see the script comments for further custom options. Once the script completes, it will generate a new object called "modevectors" (which can be changed through the options).

EXAMPLES

modevectors 1E3M, 1W7A
modevectors 1E3M, 1W7A, outname="arrows"
modevectors 1E3M, 1W7A, atom="P"

Copy/paste the following code to see an example of modevectors. This uses a multistate protein and the arrows are connected between the first and last states.

# load the code
run modevectors.py
# fetch the PDBs from pdb.org
fetch 1c3y, finish=1, multiplex=0
# separate the first and last states of the NMR ensemble to individual objects
split_states 1c3y, 1, 1
split_states 1c3y, 23, 23
hide
# run the modevectors code
modevectors 1c3y_0001, 1c3y_0023
# just setup a nice representation
as cartoon, 1c3y_0001 or 1c3y_0023
show cgo, modevectors
color marine, 1c3y_0001
color purpleblue, 1c3y_0023

The following set of examples will illustrate the power of each optional argument. Each example should be compared to the default figure in the table below.

PYMOL API

from pymol.cgo import *    # get constants
from math import *
from pymol import cmd

def modevectors( first_obj_frame, last_obj_frame, outname="modevectors", head=1.0,tail=0.3, head_length=1.5, headrgb="1.0,1.0,1.0",tailrgb="1.0,1.0,1.0",cutoff=4.0,skip=0,cut=0.5,atom="CA",stat="show",factor=1.0):
	"""
	Authors Sean Law & Srinivasa
	Michigan State University
	slaw_(at)_msu_dot_edu

	Editor Sacha Yee

	USAGE

	While in PyMOL

	load modevectors.py

	modevectors( first_obj_frame, last_obj_frame, outname=modevectors, head=1.0,tail=0.3, head_length=1.5, headrgb=(1.0,1.0,1.0),tailrgb=(1.0,1.0,1.0),cutoff=4.0,skip=0,cut=0.5,atom=CA,stat=show,factor=1.0)

	Parameter                Preset            Type    Description
	first_obj_frame          Undefined         String  Object name of the first structure.  The mode vector will propagate from this structure.  Defined by user.
	last_obj_frame           Undefined         String  Object name of the last structure.  The mode vector (arrow head) will end at this structure.  Defined by user.
	outname                  modevectors       String  Name of object to store mode vectors in.
	head                     1.0               Float   Radius for the circular base of the arrow head (cone)
	tail                     0.3               Float   Radius for the cylinder of the arrow tail (cylinder)
	head_length              1.5               Float   Length of the arrow head (from the base of the cone to the tip of cone)
	head_rgb                 1.0,1.0,1.0       String  RGB colour for the arrow head.
	tail_rgb                 1.0,1.0,1.0       String  RGB colour for the arrow tail.
	cutoff                   4.0               Float   Skips mode vectors that do not meet the cutoff distance (in Angstroms).
	skip                     0                 Integer Denotes how many atoms to skip.  No arrows will be created for skipped atoms.
	cut                      0.0               Float   Truncates all arrow tail lengths (without disturbing the arrow head) (in Angstroms).
	atom                     CA                String  Designates the atom to derive mode vectors from.
	stat                     show              String  Keeps track and prints statistics (total modevectors, skipped, cutoff).
	factor                   1.0               Float   Multiplies each mode vector length by a specified factor.
	                                                   Values between 0 and 1 will decrease the relative mode vector length.
							   Values greater than 1 will increase the relative mode vector length.
	
	"""

	framefirst=cmd.get_model(first_obj_frame)
	framelast=cmd.get_model(last_obj_frame)
	objectname=outname
	factor=float(factor)
	arrow_head_radius=float(head)
	arrow_tail_radius=float(tail)
	arrow_head_length=float(head_length)
	cutoff=float(cutoff)
	skip=int(skip)
	cut=float(cut)
	atomtype=atom.strip('"[]()')

	headrgb=headrgb.strip('" []()')
	tailrgb=tailrgb.strip('" []()')
	hr,hg,hb=map(float,headrgb.split(','))
	tr,tg,tb=map(float,tailrgb.split(','))

	pi=4*atan2(1,1)
	arrow=[]
	arrowhead = []
	arrowtail = []
	x1 = []
	y1 = []
	z1 = []
	x2 = []
	y2 = []
	z2 = []
	exit_flag=0

##############################################################
#                                                            #
# Define an object called "tail" and store the tail and  a   #
# circular base of the triangle in this object.              #
#                                                            #
##############################################################

        skipcount=0
	skipcounter=0
	keepcounter=0
	atom_lookup={}
	for atom in framefirst.atom:
		if atom.name == atomtype:
			if skipcount == skip:
				x1.append(atom.coord[0])
				y1.append(atom.coord[1])
				z1.append(atom.coord[2])
				
				##########################################
				#                                        #
				# Set atom_lookup for a specific atom    #
				# equal to ONE for the first input set.  #
				# This dictionary will be used as a      #
				# reference for the second set.          #
				#                                        #
				##########################################
				
				current_atom="CHAIN "+atom.chain+" RESID "\
					      +atom.resi+" RESTYPE "\
					      +atom.resn+\
					      " ATMNUM "+str(atom.index)
#				print current_atom
				atom_lookup['current_atom']=1
				
				skipcount=0
				keepcounter=keepcounter+1
			else:
#				print skipcount
				skipcount=skipcount+1
				skipcounter=skipcounter+1
				
        skipcount=0
	for atom in framelast.atom:
		if atom.name == atomtype:
			if skipcount == skip:
				x2.append(atom.coord[0])
				y2.append(atom.coord[1])
				z2.append(atom.coord[2])

				#########################################
				#                                       #
				# Get atom information from second set  #
				# and compare with first set.  All      #
				# atoms from this second set MUST be    #
				# found in the first set!  Otherwise,   #
				# the script will exit with an error    #
				# since modevectors can only be created #
				# by calculating values from identical  #
				# sources.                              #
				#                                       #
				#########################################
				
				current_atom="CHAIN "+atom.chain+" RESID "\
					      +atom.resi+" RESTYPE "\
					      +atom.resn+\
					      " ATMNUM "+str(atom.index)
#				print current_atom
				if atom_lookup.has_key('current_atom') != 1:
					print "\nError: "+current_atom+" from \""\
					      +last_obj_frame+\
					      " \"is not found in \""+first_obj_frame+"\"."
					print "\nPlease check your input and/or selections and try again."
					exit_flag=1
					break
					
				skipcount=0
			else:
				skipcount=skipcount+1
				
	if exit_flag == 1:
		###########################################
		#                                         #
		# Exit script because an atom cannot be   #
		# found in both input files               #
		#                                         #
		###########################################
		return
	
	cutoff_counter=0 # Track number of atoms failing to meet the cutoff

	###################################################
	#                                                 #
	# Check that the two selections/PDB files contain #
	# the same number of atoms.                       #
	#                                                 #
	###################################################

	if len(x2) != len(x1):
		print "\nError: \""+first_obj_frame+\
		      "\" and \""+last_obj_frame+\
		      "\" contain different number of residue/atoms."
		print "\nPlease check your input and/or selections and try again."
		return
	else:
		#Continue with representing modevectors!
	        #########################################
		#                                       #
		# Delete old selection or object if it  #
		# exists so that it can be overwritten  #
		#                                       #
	        #########################################
		save_view=cmd.get_view(output=1,quiet=1)
		cmd.delete(name=outname)
		cmd.hide(representation="everything",selection=first_obj_frame)
		cmd.hide(representation="everything",selection=last_obj_frame)
		


	###################################################
	#                                                 #
	# Begin drawing arrow tails                       #
	#                                                 #
	###################################################
	
	arrowtail = []
	for mv in range(len(x1)):
		vectorx=x2[mv]-x1[mv]
		vectory=y2[mv]-y1[mv]
		vectorz=z2[mv]-z1[mv]
		length=sqrt(vectorx**2+vectory**2+vectorz**2)
		if length < cutoff:
			cutoff_counter=cutoff_counter+1
			continue
		t=1.0-(cut/length)
		x2[mv]=x1[mv]+factor*t*vectorx
		y2[mv]=y1[mv]+factor*t*vectory
		z2[mv]=z1[mv]+factor*t*vectorz
		vectorx=x2[mv]-x1[mv]
		vectory=y2[mv]-y1[mv]
		vectorz=z2[mv]-z1[mv]
		length=sqrt(vectorx**2+vectory**2+vectorz**2)
		d=arrow_head_length # Distance from arrow tip to arrow base
		t=1.0-(d/length)
		tail = [
		# Tail of cylinder
		CYLINDER, x1[mv],y1[mv],z1[mv]\
		,x1[mv]+(t+0.01)*vectorx,y1[mv]+(t+0.01)*vectory,z1[mv]+(t+0.01)*vectorz\
		,arrow_tail_radius,tr,tg,tb,tr,tg,tb # Radius and RGB for each cylinder tail
		]
		arrow.extend(tail)
	
		x=x1[mv]+t*vectorx
		y=y1[mv]+t*vectory
		z=z1[mv]+t*vectorz
		dx=x2[mv]-x
		dy=y2[mv]-y
		dz=z2[mv]-z
		seg=d/100
		intfactor=int(factor)
		for i in range (100,0,-1):
			t1=seg*i
			t2=seg*(i+1)
			radius=arrow_head_radius*(1.0-i/(100.0)) #Radius of each disc that forms cone
			head=[
			CYLINDER, x+t2*dx,y+t2*dy,z+t2*dz\
			,x+t1*dx,y+t1*dy,z+t1*dz\
			,radius,hr,hg,hb,hr,hg,hb # Radius and RGB for slice of arrow head
			]
			arrow.extend(head)

##############################################################
#                                                            #
# Load the entire object into PyMOL                          #
#                                                            #
# Print statistics if requested by user                      #
#                                                            #
##############################################################

	if stat == "show":
		natoms=skipcounter+keepcounter
		print "\nTotal number of atoms = "+str(natoms)
		print "Atoms skipped = "+str(skipcounter)
		if keepcounter-cutoff_counter > 0:
			print "Atoms counted = "+str(keepcounter-cutoff_counter)+" (see PyMOL object \""+outname+"\")"
		else:
			print "Atoms counted = "+str(keepcounter-cutoff_counter)+" (Empty CGO object not loaded)"	
		print "Atoms cutoff  = "+str(cutoff_counter) #Note that cutoff occurs AFTER skipping!
	if keepcounter-cutoff_counter > 0:
		cmd.load_cgo(arrow,objectname) #Ray tracing an empty object will cause a segmentation fault.  No arrows = Do not display in PyMOL!!!
	cmd.show(representation="cartoon",selection=first_obj_frame)
	cmd.cartoon("tube")
	cmd.show(representation="cartoon",selection=last_obj_frame)
	cmd.hide(representation="cartoon",selection=last_obj_frame)
	cmd.bg_color(color="white")
	cmd.set_view(save_view)
	return

cmd.extend("modevectors",modevectors)