Tag Archives: helpful

Helpful CPPTRAJ Commands Part 2: Action Commands

The next three commands that I found to be helpful are known as Action Commands. Unlike the Topology Commands from the previous post, these Action Commands allow for a file to be created that contains the output. These commands can be used both in CPPTRAJ’s interactive mode, and in .ptraj files that can be called as inputs when starting CPPTRAJ.

 

distance [<name>] mask1 mask2 [out <filename>]

This command outputs a file that gives the distance from the center of mass of mask1 to the center of mass of mask2 at each time frame (mask1 and mask2 can either be residues or atoms). The output file will show two columns, one indicating the time frame number, and the other indicating the distance between the specified masks in Angstroms. The following visual shows a sample output of the command being called on the CA and N specified atoms (Carbon and Nitrogen respectively).

The next visual is a graph of the first 500 distance values in Angstroms in a 5000 time frame production run.

This action command can utilize other key modifiers to get slightly different outputs; however, the ones listed above are the main modifiers that are necessary to get decent data. When running CPPTRAJ on my production data on Melittin, the modifiers listed above were the only ones that I used.

Example Usage: distance sample_name1 :19@CA :19@N out sample_data1.dat 

 

hbond [<name>] [out <filename>] [<mask>] [donormask <dmask> [donorhmask <dhmask>]] [solvout <filename>] [series [uvseries <filename>]]

This action command outputs a file that shows where there was hydrogen bonding in the molecule (or specified residue or atom). Some of these modifiers are not intuitively obvious and have yet to be seen in previous action commands, so below is the list of the modifiers that we have yet to identify in this post above and what they do.

  • [donormask <dmask> [donorhmask <dhmask]] refers to a specified residue or number of atoms that will be used as solute donor heavy atoms and a specified residue or number of atoms that will be used as solute donor hydrogen atoms respectively. The second mask should only be specified if the first mask is and the two masks should have a 1 to 1 correspondence between the two masks (in my case, one mask was specified as :WAT and the other was specified as :WAT@O, which represents the water box my Melittin was being simulated in).
  • [solvout <filename>] refers to the name of a file that will be outputted containing the averaged information of the solute-solvent hydrogen bonds in the specified [<mask>]. The output file will show the average distances and average angles of the hydrogen bonds formed between the acceptor and donor atoms (both of which are shown in the output file), along with the number of times a hydrogen bond formed and the fraction of the total number of hydrogen bonds that were specified by the [<mask>].
  • [series [uvseries <filename>]] refers to the name of a file that will be outputted containing the solute-solvent hydrogen bond time data in terms of whether a hydrogen bond was formed or not (as specified by a 1 meaning a hydrogen bond was formed, and a 0 meaning a hydrogen bond was not formed).

Normally, I would include sample data; however, the outputted data yielded very odd results that may or may not be completely useless, so I would much rather not give false data until I’m able to completely figure out how this command works. There are many other modifiers for this action command, but they turned out to be useless in my case.

Example Usage: hbond sample_name2 out sample_data2.dat solventdonor :WAT solventacceptor :WAT@O solvout sample_data3.dat series uvseries sample_data4.dat

 

rms/rmsd [<name>] <mask> [out <filename>]

This action command outputs a file that contains the RMS Deviation values of a specified <mask> at each time frame. The following visual shows a small part of a sample output of the RMS Deviation values of the backbone of Tryptophan in Melittin.

The next visual is a histogram of the 5000 RMS Deviation values that were outputted from using this command on the backbone of the Tryptophan in Melittin. The y-axis represents the fraction of RMS Deviation values that made up the data, while the x-axis represents the RMS Deviation values themselves.

Example Usage: rms sample_rms :19@C,CA,N out sample_rms.dat

Leave a Comment

Filed under chemistry, computing

Helpful CPPTRAJ Commands Part 1: Topology Commands

CPPTRAJ has a variety of commands for analyzing MD Simulation outputs, but because there are so many commands it would be very difficult to describe them all in detail in a single blogpost. As such, this first post will consist of the descriptions of three Topology Commands that I found to be useful for my research of the Tryptophan residue in Melittin. These Topology Commands print out Molecular Topology related information in CPPTRAJ’s interactive mode. For all intents and purposes, the visuals used in this blogpost will strictly be regarding Melittin.

Note: [<mask>] indicates a single residue/atom or range of residues/atoms

 

atominfo [<mask>]

This command prints out general information on each atom specified by the given [<mask>] modifier. The information is outputted into 12 columns. The following visual is an example output of the command being called on the 19th residue of a Melittin .mdcrd file.

  • #Atom refers to the atom’s index as given by Amber16
  • Name refers to the atom’s name identifier as given by Amber16
  • #Res refers to the residue number in which the atom is located
  • 2nd Name refers to the shorthand name of the residue in which the atom is located
  • #Mol refers to the atom’s molecule number
  • Type refers to the type of atom in the residue (i.e. alpha, beta, etc)
  • Charge refers to the electron charge of the atom
  • Mass refers to the mass of the atom
  • GBradius refers to the generalized Born radius of the atom
  • E1 refers to the element symbol
  • rVDW refers to the Van der Waal’s force radius of the atom
  • eVDW refers to the epsilon Van der Waal’s force of the atom

Example Usage: atominfo :19

 

bondinfo [<mask>]

This command prints out general information in the form of 6 columns about each bond between each atom as specified by the [<mask>] modifier. The following visual is an example output of the command being called on a specific carbon atom in the 19th residue of a Melittin .mdcrd file.

  • Bond refers to the bond index as specified by Amber16
  • Kb refers to the bond force constant
  • Req refers to the bond equilibrium value in Angstroms
  • atom names refers to the names of the bonded atoms as specified by Amber16
  • (numbers) refers to the atom indexes as specified by Amber16 as well as the types of atoms that are bonded together

Example Usage: bondinfo :19@CA

 

resinfo [<mask>]

This command prints out general information in 7 columns about a single residue or range of residues as specified by the given [<mask>] modifier. The following visual is an example output of this command being called on the range of residues that make up Melittin. The reason I had to indicate all the residues was because the .mdcrd file that I used had Melittin simulated in a water box. If the command was called without specifying the [<mask>] modifier, the output will include the residue info for all the water molecules in the water box as well. This goes for the atominfo and bondinfo commands too.

  • #Res refers to the residue index as specified by Amber16
  • Name refers to the shorthand name for each residue
  • First refers to the atom index of the first atom in the residue
  • Last refers to the atom index of the last atom in the residue
  • Natom refers to the number of atoms in the residue
  • #Orig refers to the original residue number in the original PDB file of which the date comes from
  • #Mol refers to the molecule number

One can also add the modifier, [short], to display the residues in the FASTA code sequence form. For Melittin, the sequence would look like this: GIGAVLKVLTTGLPALISWIKRKRQQ.

Example Usage: resinfo :1-26

 

Leave a Comment

Filed under chemistry, computing