Pairwise distances

Introduction

Given any two selections, this script calculates and returns the pairwise distances between all atoms that fall within a defined distance.

Can be used to measure distances within the same chain, between different chains or different objects.

Distances can be restricted to sidechain atoms only and the outputs either displayed on screen or printed on file.

Usage

pairwise_dist sel1, sel2, max_dist, [output=S/P/N, [sidechain=N/Y, [show=Y/N]]]

Required Arguments

• sel1 = first selection
• sel2 = second selection
• max_dist = max distance in Angstroms

Optional Arguments

• output = accepts Screen/Print/None (default N)
• sidechain = limits (Y) results to sidechain atoms (default N)
• show = shows (Y) individual distances in pymol menu (default=N)

Examples

example #1

PyMOL>pairwise_dist 1efa and chain D, 1efa and chain B, 3, output=S, show=Y
 
1efa/D/DC/13/OP1 to 1efa/B/TYR/47/OH: 2.765
1efa/D/DC/13/OP2 to 1efa/B/LEU/6/N: 2.983
1efa/D/DC/13/OP2 to 1efa/B/LEU/6/CB: 2.928
1efa/D/DT/14/O4' to 1efa/B/ALA/57/CB: 2.827
1efa/D/DT/14/OP1 to 1efa/B/ASN/25/OD1: 2.858
1efa/D/DT/14/OP1 to 1efa/B/GLN/54/NE2: 2.996
1efa/D/DT/14/OP2 to 1efa/B/SER/21/OG: 2.517
1efa/D/DC/15/N4 to 1efa/B/GLN/18/NE2: 2.723
1efa/D/DA/16/N6 to 1efa/B/GLN/18/NE2: 2.931
 
Number of distances calculated: 9

example #2

PyMOL>pairwise_dist 2w8s and chain a, 2W8s and chain b, 3, sidechain=Y, output=S, show=Y
 
2W8S/A/GLN/432/OE1 to 2W8S/B/ARG/503/NH2: 2.758
2W8S/A/ASP/434/OD1 to 2W8S/B/SER/493/OG: 2.444
2W8S/A/TYR/447/OH to 2W8S/B/GLN/485/NE2: 2.878
2W8S/A/HIS/449/NE2 to 2W8S/B/SER/489/OG: 2.686
2W8S/A/GLN/485/OE1 to 2W8S/B/TYR/447/OH: 2.971
2W8S/A/SER/489/OG to 2W8S/B/HIS/449/NE2: 2.913
2W8S/A/SER/493/OG to 2W8S/B/ASP/434/OD1: 2.491
2W8S/A/ARG/503/NH2 to 2W8S/B/GLN/432/OE1: 2.653
 
Number of distances calculated: 8

example #3

PyMOL>pairwise_dist 1FOS and chain H and resi 290:300, 1FOS and chain G, 4, sidechain=Y, show=Y, output=P
 
Results saved in IntAtoms_4.txt
Number of distances calculated: 24

The Code

Copy the following text and save it as pairwisedistances.py

from pymol import cmd, stored, math

def pairwise_dist(sel1, sel2, max_dist, output="N", sidechain="N", show="N"):
	"""
	usage: pairwise_dist sel1, sel2, max_dist, [output=S/P/N, [sidechain=N/Y, [show=Y/N]]]
	sel1 and sel2 can be any to pre-existing or newly defined selections
	max_dist: maximum distance in Angstrom between atoms in the two selections
	--optional settings:
	output: accepts Screen/Print/None (default N)
	sidechain: limits (Y) results to sidechain atoms (default N)
	show: shows (Y) individual distances in pymol menu (default=N)
	"""
	print ""
	cmd.delete ("dist*")
	extra=""
	if sidechain=="Y": extra=" and not name c+o+n"
	
	#builds models
	m1=cmd.get_model(sel2+" around "+str(max_dist)+" and "+sel1+extra)
	m1o=cmd.get_object_list(sel1)
	m2=cmd.get_model(sel1+" around "+str(max_dist)+" and "+sel2+extra)
	m2o=cmd.get_object_list(sel2)

	#defines selections
	cmd.select("__tsel1a", sel1+" around "+str(max_dist)+" and "+sel2+extra)
	cmd.select("__tsel1", "__tsel1a and "+sel2+extra)
	cmd.select("__tsel2a", sel2+" around "+str(max_dist)+" and "+sel1+extra)
	cmd.select("__tsel2", "__tsel2a and "+sel1+extra)
	cmd.select("IntAtoms_"+max_dist, "__tsel1 or __tsel2")
	cmd.select("IntRes_"+max_dist, "byres IntAtoms_"+max_dist)
 
	#controlers-1
	if len(m1o)==0: 
		print "warning, '"+sel1+extra+"' does not contain any atoms."
		return
	if len(m2o)==0: 
		print "warning, '"+sel2+extra+"' does not contain any atoms."
		return
	
	#measures distances
	s=""
	counter=0
	for c1 in range(len(m1.atom)):
		for c2 in range(len(m2.atom)):
			distance=math.sqrt(sum(map(lambda f: (f[0]-f[1])**2, zip(m1.atom[c1].coord,m2.atom[c2].coord))))
			if distance<float(max_dist):
				s+="%s/%s/%s/%s/%s to %s/%s/%s/%s/%s: %.3f\n" % (m1o[0],m1.atom[c1].chain,m1.atom[c1].resn,m1.atom[c1].resi,m1.atom[c1].name,m2o[0],m2.atom[c2].chain,m2.atom[c2].resn,m2.atom[c2].resi,m2.atom[c2].name, distance)
				counter+=1
				if show=="Y": cmd.distance (m1o[0]+" and "+m1.atom[c1].chain+"/"+m1.atom[c1].resi+"/"+m1.atom[c1].name, m2o[0]+" and "+m2.atom[c2].chain+"/"+m2.atom[c2].resi+"/"+m2.atom[c2].name)

	#controler-2
	if counter==0: 
		print "warning, no distances were measured! Check your selections/max_dist value"
		return
	
	#outputs
	if output=="S": print s
	if output=="P":
		f=open('IntAtoms_'+max_dist+'.txt','w')
		f.write("Number of distances calculated: %s\n" % (counter))
		f.write(s)
		f.close()
		print "Results saved in IntAtoms_%s.txt" % max_dist
	print "Number of distances calculated: %s" % (counter)
	cmd.hide("lines", "IntRes_*")
	if show=="Y": cmd.show("lines","IntRes_"+max_dist)
	cmd.deselect()
  
cmd.extend("pairwise_dist", pairwise_dist)