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Unverified Commit 466a826e authored by peastman's avatar peastman Committed by GitHub
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Merge pull request #2448 from JoaoRodrigues/restrain_existing_H 

Restraint existing atoms during addHydrogens
parents c7441b96 46b334ce
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Showing with 86 additions and 37 deletions
wrappers/python/simtk/openmm/app/modeller.py
View file @ 466a826e
......@@ -712,6 +712,8 @@ class Modeller(object):
automatically, this function will only add hydrogens. It will never remove ones that are already present in the
model, regardless of the specified pH.
In all cases, the positions of existing atoms (including existing hydrogens) are not modified.
Definitions for standard amino acids and nucleotides are built in. You can call loadHydrogenDefinitions() to load
additional definitions for other residue types.
......@@ -930,14 +932,16 @@ class Modeller(object):
# The hydrogens were added at random positions. Now perform an energy minimization to fix them up.
addedH = set(newIndices) # keep track of Hs added
if forcefield is not None:
# Use the ForceField the user specified.
system = forcefield.createSystem(newTopology, rigidWater=False, nonbondedMethod=CutoffNonPeriodic)
atoms = list(newTopology.atoms())
for i in range(system.getNumParticles()):
if atoms[i].element != elem.hydrogen:
# This is a heavy atom, so make it immobile.
if i not in addedH:
# Existing atom, make it immobile.
system.setParticleMass(i, 0)
else:
# Create a System that restrains the distance of each hydrogen from its parent atom
......@@ -955,7 +959,7 @@ class Modeller(object):
bondedTo = []
for atom in newTopology.atoms():
nonbonded.addParticle([])
if atom.element != elem.hydrogen:
if atom.index not in addedH: # make immobile
system.addParticle(0.0)
else:
system.addParticle(1.0)
......@@ -1221,33 +1225,33 @@ class Modeller(object):
def addMembrane(self, forcefield, lipidType='POPC', membraneCenterZ=0*nanometer, minimumPadding=1*nanometer, positiveIon='Na+', negativeIon='Cl-', ionicStrength=0*molar, neutralize=True):
"""Add a lipid membrane to the model.
This method actually adds both a membrane and a water box. It is best to build them together,
both to avoid adding waters inside the membrane and to ensure that lipid head groups are properly
solvated. For that reason, this method includes many of the same arguments as addSolvent().
The membrane is added in the XY plane, and the existing protein is assumed to already be oriented
and positioned correctly. When possible, it is recommended to start with a model from the
Orientations of Proteins in Membranes (OPM) database at http://opm.phar.umich.edu. Otherwise, it
is up to you to select the protein position yourself.
The algorithm is based on the one described in Wolf et al., J. Comp. Chem. 31, pp. 2169-2174 (2010).
It begins by tiling copies of a pre-equilibrated membrane patch to create a membrane of the desired
size. Next it scales down the protein by 50% along the X and Y axes. Any lipid within a cutoff
distance of the scaled protein is removed. It also ensures that equal numbers of lipids are removed
from each leaf of the membrane. Finally, 1000 steps of molecular dynamics are performed to let
the membrane relax while the protein is gradually scaled back up to its original size.
The size of the membrane and water box are determined by the minimumPadding argument. All
pre-existing atoms are guaranteed to be at least this far from any edge of the periodic box. It
is also possible for the periodic box to have more padding than requested. In particular, it only
adds whole copies of the pre-equilibrated membrane patch, so the box dimensions will always be
integer multiples of the patch size. That may lead to a larger membrane than what you requested.
This method has built in support for POPC and POPE lipids. You can also build other types of
membranes by providing a pre-equilibrated, solvated membrane patch that can be tiled in the XY
plane to form the membrane.
Parameters
----------
forcefield : ForceField
......@@ -1282,8 +1286,8 @@ class Modeller(object):
membraneCenterZ = membraneCenterZ.value_in_unit(nanometer)
if is_quantity(minimumPadding):
minimumPadding = minimumPadding.value_in_unit(nanometer)
# Figure out how many copies of the membrane patch we need in each direction.
# Figure out how many copies of the membrane patch we need in each direction.
proteinPos = self.positions.value_in_unit(nanometer)
proteinMinPos = Vec3(*[min((p[i] for p in proteinPos)) for i in range(3)])
......@@ -1298,15 +1302,15 @@ class Modeller(object):
patchCenterPos = (patchMinPos+patchMaxPos)/2
nx = int(ceil((proteinSize[0]+2*minimumPadding)/patchSize[0]))
ny = int(ceil((proteinSize[1]+2*minimumPadding)/patchSize[1]))
# Record the bonds for each residue.
resBonds = defaultdict(list)
for bond in patch.topology.bonds():
resBonds[bond[0].residue].append(bond)
# Identify which leaf of the membrane each lipid is in.
numLipidAtoms = 0
resMeanZ = {}
membraneMeanZ = 0.0
......@@ -1322,17 +1326,17 @@ class Modeller(object):
resMeanZ[res] = sumZ/numResAtoms
membraneMeanZ /= numLipidAtoms
lipidLeaf = dict((res, 0 if resMeanZ[res] < membraneMeanZ else 1) for res in resMeanZ)
# Compute scaled positions for the protein.
scaledProteinPos = [None]*len(proteinPos)
for i, p in enumerate(proteinPos):
p = p-proteinCenterPos
p = Vec3(0.5*p[0], 0.5*p[1], p[2])
scaledProteinPos[i] = p+proteinCenterPos
# Create a new Topology for the membrane.
membraneTopology = Topology()
membranePos = []
boxSizeZ = patchSize[2]
......@@ -1341,12 +1345,12 @@ class Modeller(object):
else:
boxSizeZ = max(boxSizeZ, proteinSize[2]+2*minimumPadding)
membraneTopology.setUnitCellDimensions((nx*patchSize[0], ny*patchSize[1], boxSizeZ))
# Add membrane patches. We exclude any water that is within a cutoff distance of either the actual or scaled
# protein, and any lipid that is within a cutoff distance of the scaled protein. We also keep track of how
# many lipids have been excluded from each leaf of the membrane, so we can make sure exactly the same
# number get removed from each leaf.
overlapCutoff = 0.22
chain = membraneTopology.addChain()
addedWater = []
......@@ -1395,9 +1399,9 @@ class Modeller(object):
del cellLists
del cells
del proteinCells
# Add the lipids.
newAtoms = {}
lipidChain = membraneTopology.addChain()
lipidResNum = 1 # renumber lipid residues to handle large patches
......@@ -1408,7 +1412,7 @@ class Modeller(object):
else:
newResidue = membraneTopology.addResidue(residue.name, lipidChain, lipidResNum, residue.insertionCode)
lipidResNum += 1
for atom in residue.atoms():
newAtom = membraneTopology.addAtom(atom.name, atom.element, newResidue, atom.id)
newAtoms[atom] = newAtom
......@@ -1418,9 +1422,9 @@ class Modeller(object):
del lipidLeaf
del addedLipids
# Add the solvent.
solventChain = membraneTopology.addChain()
for (residue, pos) in addedWater:
newResidue = membraneTopology.addResidue(residue.name, solventChain, residue.id, residue.insertionCode)
......@@ -1436,7 +1440,7 @@ class Modeller(object):
gc.collect()
# Create a System for the lipids, then add in the protein as stationary particles.
system = forcefield.createSystem(membraneTopology, nonbondedMethod=CutoffPeriodic)
proteinSystem = forcefield.createSystem(self.topology, nonbondedMethod=CutoffNonPeriodic)
numMembraneParticles = system.getNumParticles()
......@@ -1458,9 +1462,9 @@ class Modeller(object):
del membranePos
del scaledProteinCells
gc.collect()
# Run a simulation while slowly scaling up the protein so the membrane can relax.
integrator = LangevinIntegrator(10.0, 50.0, 0.001)
context = Context(system, integrator)
context.setPositions(mergedPositions)
......@@ -1483,24 +1487,24 @@ class Modeller(object):
mergedPositions[j+numMembraneParticles] = (weight1*proteinPos[j] + weight2*scaledProteinPos[j])
context.setPositions(mergedPositions)
integrator.step(20)
# Add the membrane to the protein.
modeller = Modeller(self.topology, self.positions)
modeller.add(membraneTopology, context.getState(getPositions=True).getPositions()[:numMembraneParticles])
modeller.topology.setPeriodicBoxVectors(membraneTopology.getPeriodicBoxVectors())
del context
del system
del integrator
# Depending on the box size, we may need to add more water beyond what was included with the membrane patch.
needExtraWater = (boxSizeZ > patchSize[2])
if needExtraWater:
modeller.addSolvent(forcefield, neutralize=False)
# Record the positions of all waters that have been added.
waterPos = {}
for chain in list(modeller.topology.chains())[-2:]:
for residue in chain.residues():
......@@ -1564,7 +1568,7 @@ class Modeller(object):
class _CellList(object):
"""This class organizes atom positions into cells, so the neighbors of a point can be quickly retrieved"""
def __init__(self, positions, maxCutoff, vectors, periodic):
self.positions = positions[:]
self.cells = {}
......
wrappers/python/tests/TestModeller.py
View file @ 466a826e
......@@ -593,6 +593,51 @@ class TestModeller(unittest.TestCase):
validate_equivalence(self, topology_start, topology_after)
def test_addHydrogensPdb3_keepPositions(self):
""" Test addHydrogens() does not change existing Hs positions """
# build the Modeller
topology_start = self.topology_start3
positions = self.positions3.value_in_unit(nanometers)
modeller = Modeller(topology_start, positions)
# Record original hydrogen positions
oriH = [atom.index for atom in modeller.topology.atoms() if atom.element == element.hydrogen]
oriH_pos = [positions[i] for i in oriH]
# Remove hydrogens from last residue
res_list = list(topology_start.residues())
toDelete = [atom for atom in res_list[-1].atoms() if atom.element == element.hydrogen]
modeller.delete(toDelete)
n_deleted = len(toDelete)
# Add hydrogen atoms back.
modeller.addHydrogens(self.forcefield)
topology_after = modeller.getTopology()
# Fetch 'new' positions
new_positions = modeller.positions.value_in_unit(nanometers)
newH = [atom.index for atom in topology_after.atoms() if atom.element == element.hydrogen]
newH_pos = [new_positions[i] for i in newH]
# Did we add all Hs back in correctly?
self.assertEqual(len(newH), len(oriH))
# Are the old ones at the same position?
# Negative control
oriH_fixed = oriH_pos[:-1*n_deleted]
newH_fixed = newH_pos[:-1*n_deleted]
xyz_diff = any([norm(o-n) > 1e-6 for o, n in zip(oriH_fixed, newH_fixed)])
self.assertEqual(xyz_diff, False)
# Were the new ones optimized?
# Positive control
oriH_added = oriH_pos[-1*n_deleted:]
newH_added = newH_pos[-1*n_deleted:]
xyz_diff = all([norm(o-n) > 1e-6 for o, n in zip(oriH_added, newH_added)])
self.assertEqual(xyz_diff, True)
def test_addHydrogensASH(self):
""" Test of addHydrogens() in which we force ASH to be a variant using the variants parameter. """
......@@ -1079,7 +1124,7 @@ class TestModeller(unittest.TestCase):
def test_addMembrane(self):
"""Test adding a membrane to a realistic system."""
mol = PDBxFile('systems/gpcr.cif')
modeller = Modeller(mol.topology, mol.positions)
ff = ForceField('amber14-all.xml', 'amber14/tip3p.xml')
......
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