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# This example shows how to build a multicomponent spherical vesicle.
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# The lipid bilayer is composed of two different lipids (DPPC and DLPC),
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# The vesicle contains 120 trans-membrane protein inclusions.
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# The DPPC lipid model is described here:
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# G. Brannigan, P.F. Philips, and F.L.H. Brown,
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# Physical Review E, Vol 72, 011915 (2005)
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# The protein model is described here:
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# G. Bellesia, AI Jewett, and J-E Shea,
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# Protein Science, Vol19 141-154 (2010)
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# The new DLPC model is a truncated version of DPPC,
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# (Its behaviour has not been rigorously tested.)
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# Note that 50%/50% mixtures of DPPC & DLPC are commonly used to
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# build liposomes http://www.ncbi.nlm.nih.gov/pubmed/10620293
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# NOTE: THE COORDINATES FOR THESE MOLECULES ARE GENERATED BY PACKMOL (see below)
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# This example may require additional features to be added to LAMMPS.
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# If LAMMPS complains about an "Invalid pair_style", then copy the code
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# in the "additional_lammps_code" directory into your LAMMPS "src" directory
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# and recompile LAMMPS.
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# First, load the definitions of the molecules we will need:
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import "CGLipidBr2005.lt"
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using namespace CGLipidBr2005
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import "1beadProtSci2010.lt"
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using namespace 1beadProtSci2010
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# Coordinates for the molecules in this example are loaded from an .XYZ file
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# created by PACKMOL. This must be done in advance. (See ../packmol_files/)
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# The XYZ file was created by PACKMOL in 3 steps:
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# (Add the proteins, then pack lipids in the inner & outer layers around them.)
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# step1) Creae 120 proteins. Distribute them on the surface of the sphere.
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# step2) Keeping the coordinates from step1 fixed,
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# a) first we add 9500 DPPC lipids to the inner monolayer
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# b) then we add 9500 DLPC lipids to the inner monolayer
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# step3) Keeping the coordinates from steps 1 and 2 fixed,
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# a) first we add 12500 DPPC lipids to the outer monolayer
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# b) then we add 12500 DLPC lipids to the outer monolayer
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# The order that molecules are created in moltemplate should match the order
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# they appear in the final XYZ file created by PACKMOL. (See above.)
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# Consequently I instantiate the molecules in the same order here:
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# Step 1) ---- protein inclusions ----
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proteins = new 4HelixInsideOut [120]
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# Step 2a) ---- inner monolayer ----
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dppc_in = new DPPC [9500]
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dlpc_in = new DLPC [9500]
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# Step 3a) ---- outer monolayer ----
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dppc_out = new DPPC [12500]
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dlpc_out = new DLPC [12500]
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# ------------------ boundary conditions --------------------
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write_once("Data Boundary") {
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write_once("In Settings") {
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# -----------------------------------------------------------
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# -------- interactions between protein and lipids ----------
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# -----------------------------------------------------------
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# Interactions between the protein and lipid atoms are usually
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# determined by mixing rules. (However this is not possible some
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# for atoms, such as the "int" atoms in the lipid model which
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# interact using -1/r^2 attraction.) Mixing rules do not make
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# sense for these atoms so we must explicitly define their
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# interaction with all other atoms.
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# We want the hydrophobic interactions between hydrophobic residues in
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# the protein and beads the interior of the lipid to be energetically
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# similar to the attractive interactions between the lipid tails.
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# Note: I made the width of the outward-facing protein beads slightly larger
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# ("12.5") whenever they interact with the "tail" beads in each lipid
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# (in order to make the protein wider there).
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# This hopefully relieves some of the internal negative pressure in the center
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# of the bilayer which can otherwise rip apart the protein or suck it into
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# the bilaer. (This is a hack, and I'm not sure if it is necessary.
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# For different protein or lipid models, you probably don't need this.)
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# i j pairstylename eps sig K L
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pair_coeff @atom:CGLipidBr2005/tail @atom:1beadProtSci2010/sH lj/charmm/coul/charmm/inter 0.1643 12.5 0.4 -1
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pair_coeff @atom:CGLipidBr2005/int @atom:1beadProtSci2010/sH lj/charmm/coul/charmm/inter 0.1643 7.5 0.4 -1
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# To help keep the protein from tilting 90 degrees and burying itself
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# within the lipid bilayer, we make the turn regions at either
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# end of the protein (strongly) attracted to the head groups
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# of the lipid. (In reality, they would probably be attracted
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# to the water as well.)
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pair_coeff @atom:CGLipidBr2005/DPPC/head @atom:1beadProtSci2010/tN lj/charmm/coul/charmm/inter 1.8065518 5.5 1 -1
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pair_coeff @atom:CGLipidBr2005/DPPC/head @atom:1beadProtSci2010/tN lj/charmm/coul/charmm/inter 1.8065518 5.5 1 -1
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# All other interactions between proteins and lipids are steric.
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pair_coeff @atom:CGLipidBr2005/tail @atom:1beadProtSci2010/sL lj/charmm/coul/charmm/inter 0.1643 7.5 0.4 0
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pair_coeff @atom:CGLipidBr2005/tail @atom:1beadProtSci2010/tN lj/charmm/coul/charmm/inter 0.1643 7.5 0.4 0
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pair_coeff @atom:CGLipidBr2005/int @atom:1beadProtSci2010/sL lj/charmm/coul/charmm/inter 0.1643 7.5 0.4 0
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pair_coeff @atom:CGLipidBr2005/int @atom:1beadProtSci2010/tN lj/charmm/coul/charmm/inter 0.1643 7.5 0.4 0
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pair_coeff @atom:CGLipidBr2005/DPPC/head @atom:1beadProtSci2010/sH lj/charmm/coul/charmm/inter 0.1643 7.5 0.4 0
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pair_coeff @atom:CGLipidBr2005/DPPC/head @atom:1beadProtSci2010/sL lj/charmm/coul/charmm/inter 0.1643 7.5 0.4 0
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pair_coeff @atom:CGLipidBr2005/DLPC/head @atom:1beadProtSci2010/sH lj/charmm/coul/charmm/inter 0.1643 7.5 0.4 0
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pair_coeff @atom:CGLipidBr2005/DLPC/head @atom:1beadProtSci2010/sL lj/charmm/coul/charmm/inter 0.1643 7.5 0.4 0
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# -----------------------------------------------------------
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# -------- Modifications to the protein model: --------------
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# -----------------------------------------------------------
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# Turn off attraction between the hydrophobic "@atom:sH" beads:
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# (These beads are located in the outside of a trans-membrane protein.)
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pair_coeff @atom:1beadProtSci2010/sH @atom:1beadProtSci2010/sH lj/charmm/coul/charmm/inter 1.8065518 5.5 1 0
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# (Why: These beads are only attracted to
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# each other in an aqueous environment)
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# Turn ON attraction between the hydrophilic "@atom:sL" beads.
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# (These beads are located in the interior of a trans-membrane protein.)
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pair_coeff @atom:1beadProtSci2010/sL @atom:1beadProtSci2010/sL lj/charmm/coul/charmm/inter 1.8065518 5.5 1 -1
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# In reality, polar groups in the interior of trans-membrane
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# proteins do form hydrogen bonds with each other. This was
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# absent from the original protein model because, in an aqueous
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# environment, these groups preferentially interact with the water.
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# Why is this necessary?
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# Shouldn't attraction between lipid tails and the protein create
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# an effective force which brings the hydrophilic beads together?
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# (similar to the hydrophobic effect, but in reverse?).
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# Unlike an aqueous environment (~zero pressure, or +1atm), there is
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# a large negative pressure in the interior of some bilayer membrane
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# models (such as this one). Without some kind of direct attraction
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# between interior residues, the protein will get pulled apart.
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# (Perhaps the attractive force I am using is too strong?)
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# Finally, we must combine the two force-field styles which were used for
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# the coarse-grained lipid and protein. To do that, we write one last time
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# to the "In Init" section. When reading the "Init" section LAMMPS will
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# read these commands last and this will override any earlier settings.
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write_once("In Init") {
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# -- These styles override earlier settings --
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# (Hybrid force field styles were used for portability.)
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bond_style hybrid harmonic
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angle_style hybrid cosine/delta harmonic
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dihedral_style hybrid fourier
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pair_style hybrid table linear 1130 lj/charmm/coul/charmm/inter es4k4l 14.5 15
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pair_modify mix arithmetic
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special_bonds lj 0.0 0.0 1.0 # turn off pairs if "less than 3 bonds"