helix_kinks.py

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"""
Functions to calculate helix kinks: bend, face shift and wobbla angles

Author: Niklaus Johner
"""

import os
import ost

def __FindProline(sele,proline):
  if not sele.IsValid():
    print 'selection is not valid'
    raise RuntimeError
  if proline==False:
    proline=sele.Select('rname=PRO')
  if not proline.GetResidueCount()==1:
    print proline.GetResidueCount(),'prolines in the selection. One proline is needed'
    raise RuntimeError
  proline=proline.residues[0]
  proline_ca=proline.FindAtom('CA')
  if not proline_ca.IsValid():
    print 'proline has no CA atom'
    raise RuntimeError
  return (proline,proline_ca)
  proline.GetNumber().num
  
def __SelectPreAndPostProline(sele,proline_num):
  pre_proline=sele.Select('rnum<'+str(proline_num))
  post_proline=sele.Select('rnum>'+str(proline_num))
  print 'pre-proline residues'
  for res in pre_proline.residues:
    print res
  print 'post-proline residues'
  for res in post_proline.residues:
    print res
  if pre_proline.GetResidueCount()<4 or post_proline.GetResidueCount()<4:
    print 'pre and post proline helices should be at least 4 residues long, 7 for better stability'
    raise RuntimeError
  return (pre_proline,post_proline)

def __FindCa3AndCa4(sele,proline_ca,proline_num):
  ca_3=sele.FindAtom(proline_ca.GetHandle().GetChain().GetName(),proline_num-3,'CA')
  ca_4=sele.FindAtom(proline_ca.GetHandle().GetChain().GetName(),proline_num-4,'CA')
  if not (ca_3.IsValid() and ca_4.IsValid()):
    print 'CA not found in (i-4) or (i-3) residue'
    raise RuntimeError
  return (ca_3,ca_4)


def __CalculateBendAngle(pre_proline_axis,post_proline_axis):
  return ost.geom.Angle(pre_proline_axis,post_proline_axis)
  
def __CalculateWobbleAngle(pre_proline_axis,post_proline_axis,post_proline_centers,proline_pos):
  p1=proline_pos-post_proline_centers
  n1=p1-ost.geom.Dot(p1,post_proline_axis)*post_proline_axis
  p2=-pre_proline_axis
  n2=p2-ost.geom.Dot(p2,post_proline_axis)*post_proline_axis
  sign=ost.geom.Dot(ost.geom.Cross(pre_proline_axis,n2),n2-n1)
  sign=sign/abs(sign)
  return sign*ost.geom.Angle(n1,n2)

def __CalculateFaceShift(pre_proline_axis,post_proline_axis,pre_proline_centers,post_proline_centers,proline_pos,ca3_pos,ca4_pos,bend_angle):
  p1=proline_pos-post_proline_centers
  n1=p1-ost.geom.Dot(p1,post_proline_axis)*post_proline_axis
  p2=(ca3_pos+ca4_pos)/2.0-pre_proline_centers
  n2=p2-ost.geom.Dot(p2,pre_proline_axis)*pre_proline_axis
  #Here we want to apply a rotation to n1, to align the post-proline axis on the pre-proline axis
  R=ost.geom.AxisRotation(ost.geom.Cross(post_proline_axis,pre_proline_axis),bend_angle)
  n1=R*n1
  #We also need to determine the sign of the angle
  sign=ost.geom.Dot(ost.geom.Cross(pre_proline_axis,n2),n2-n1)
  sign=sign/abs(sign)
  return sign*ost.geom.Angle(n1,n2)


def AnalyzeHelixKink(t,sele,proline=False):
  """
  This function calculates the bend,wobble and face-shift angles
  in an alpha-helix over a trajectory. The determination is more stable if
  there are at least 4 residues on each side (8 is even better) of the prolin around which
  the helix is kinked. The selection should contain all residues in the correct
  order and with no gaps and no missing C-alphas.
  Input:
    t     : The trajectory to be analyzed (CoordGroup)
    sele  : A selection containing the alpha helix to be analyzed (EntityView)
    proline=False : An EntityView containing only the proline (or another residue) around which the
                    helix is kinked. If False, the proline will be serached for automatically
  Output:
    (bend_angle,face_shift,wobble_angle) : a tuple of FloatLists
  """
  n_frames=t.GetFrameCount()
  (proline,proline_ca)=__FindProline(sele,proline)
  proline_num=proline.GetNumber().num
  (pre_proline,post_proline)=__SelectPreAndPostProline(sele,proline_num)
  (ca_3,ca_4)=__FindCa3AndCa4(sele,proline_ca,proline_num)
  #Here we extract the necessary information from the trajectory
  pre_proline_axis=ost.geom.Vec3List()
  post_proline_axis=ost.geom.Vec3List()
  pre_proline_centers=ost.geom.Vec3List()
  post_proline_centers=ost.geom.Vec3List()
  ost.mol.alg.AnalyzeAlphaHelixAxis(t,pre_proline,pre_proline_axis,pre_proline_centers)
  ost.mol.alg.AnalyzeAlphaHelixAxis(t,post_proline,post_proline_axis,post_proline_centers)
  proline_pos=ost.mol.alg.AnalyzeAtomPos(t,proline_ca.GetHandle())
  ca3_pos=ost.mol.alg.AnalyzeAtomPos(t,ca_3.GetHandle())
  ca4_pos=ost.mol.alg.AnalyzeAtomPos(t,ca_4.GetHandle())
  #Now we calculate the bend angle
  bend_angle=[]
  face_shift=[]
  wobble_angle=[]
  for i in range(n_frames):
    bend_angle.append(__CalculateBendAngle(pre_proline_axis[i],post_proline_axis[i]))
    face_shift.append(__CalculateFaceShift(pre_proline_axis[i],post_proline_axis[i],pre_proline_centers[i],post_proline_centers[i],proline_pos[i],ca3_pos[i],ca4_pos[i],bend_angle[i]))
    wobble_angle.append(__CalculateWobbleAngle(pre_proline_axis[i],post_proline_axis[i],post_proline_centers[i],proline_pos[i]))
  return (bend_angle,face_shift,wobble_angle)


def CalculateHelixKink(sele,proline=False):
  """
  This function calculates the bend,wobble and face-shift angles
  in an alpha-helix of an EntityView. The determination is more stable if
  there are at least 4 residues on each side (8 is even better) of the prolin around which
  the helix is kinked. The selection should contain all residues in the correct
  order and with no gaps and no missing C-alphas.
  Input:
    sele  : A selection containing the alpha helix to be analyzed (EntityView)
    proline=False : An EntityView containing only the proline (or another residue) around which the
                    helix is kinked. If False, the proline will be serached for automatically
  Output:
    (bend_angle,face_shift,wobble_angle) : a tuple of Floats
  """
  (proline,proline_ca)=__FindProline(sele,proline)
  proline_num=proline.GetNumber().num
  (pre_proline,post_proline)=__SelectPreAndPostProline(sele,proline_num)
  (ca_3,ca_4)=__FindCa3AndCa4(sele,proline_ca,proline_num)  
  #Here we extract the necessary information from the structure
  pre_proline_axis=ost.mol.alg.structure_analysis.CalculateHelixAxis(pre_proline)
  post_proline_axis=ost.mol.alg.structure_analysis.CalculateHelixAxis(post_proline)
  prepa=pre_proline_axis.GetDirection()
  prepc=pre_proline_axis.GetOrigin()
  postpa=post_proline_axis.GetDirection()
  postpc=post_proline_axis.GetOrigin()
  #calculate the angles
  bend=__CalculateBendAngle(prepa,postpa)
  wobble=__CalculateWobbleAngle(prepa,postpa,postpc,proline_ca.pos)
  shift=__CalculateFaceShift(prepa,postpa,prepc,postpc,proline_ca.pos,ca_3.pos,ca_4.pos,bend)
  return (bend,shift,wobble)