gmx-helixorient(1) GROMACS Manual gmx-helixorient(1)NAMEgmx-helixorient - Calculate local pitch/bending/rotation/orientation
inside helices
SYNOPSIS
gmx helixorient [-s [<.tpr/.tpb/...>]] [-f [<.xtc/.trr/...>]]
[-n [<.ndx>]] [-oaxis [<.dat>]] [-ocenter [<.dat>]]
[-orise [<.xvg>]] [-oradius [<.xvg>]] [-otwist [<.xvg>]]
[-obending [<.xvg>]] [-otilt [<.xvg>]] [-orot [<.xvg>]]
[-nice <int>] [-b <time>] [-e <time>] [-dt <time>]
[-xvg <enum>] [-[no]sidechain] [-[no]incremental]
DESCRIPTION
gmx helixorient calculates the coordinates and direction of the average
axis inside an alpha helix, and the direction/vectors of both the Cal‐
pha and (optionally) a sidechain atom relative to the axis.
As input, you need to specify an index group with Calpha atoms corre‐
sponding to an alpha-helix of continuous residues. Sidechain directions
require a second index group of the same size, containing the heavy
atom in each residue that should represent the sidechain.
Note that this program does not do any fitting of structures.
We need four Calpha coordinates to define the local direction of the
helix axis.
The tilt/rotation is calculated from Euler rotations, where we define
the helix axis as the local x-axis, the residues/Calpha vector as y,
and the z-axis from their cross product. We use the Euler Y-Z-X rota‐
tion, meaning we first tilt the helix axis (1) around and (2) orthogo‐
nal to the residues vector, and finally apply the (3) rotation around
it. For debugging or other purposes, we also write out the actual Euler
rotation angles as theta[1-3].xvg
OPTIONS
Options to specify input and output files:
-s [<.tpr/.tpb/...>] (topol.tpr) (Input)
Run input file: tpr tpb tpa
-f [<.xtc/.trr/...>] (traj.xtc) (Input)
Trajectory: xtc trr cpt trj gro g96 pdb tng
-n [<.ndx>] (index.ndx) (Input, Optional)
Index file
-oaxis [<.dat>] (helixaxis.dat) (Output)
Generic data file
-ocenter [<.dat>] (center.dat) (Output)
Generic data file
-orise [<.xvg>] (rise.xvg) (Output)
xvgr/xmgr file
-oradius [<.xvg>] (radius.xvg) (Output)
xvgr/xmgr file
-otwist [<.xvg>] (twist.xvg) (Output)
xvgr/xmgr file
-obending [<.xvg>] (bending.xvg) (Output)
xvgr/xmgr file
-otilt [<.xvg>] (tilt.xvg) (Output)
xvgr/xmgr file
-orot [<.xvg>] (rotation.xvg) (Output)
xvgr/xmgr file
Other options:
-nice <int> (19)
Set the nicelevel
-b <time> (0)
First frame (ps) to read from trajectory
-e <time> (0)
Last frame (ps) to read from trajectory
-dt <time> (0)
Only use frame when t MOD dt = first time (ps)
-xvg <enum> (xmgrace)
xvg plot formatting: xmgrace, xmgr, none
-[no]sidechain (no)
Calculate sidechain directions relative to helix axis too.
-[no]incremental (no)
Calculate incremental rather than total rotation/tilt.
SEE ALSOgromacs(7)
More information about GROMACS is available at <http://www.gro‐
macs.org/>.
VERSION 5.0.6gmx-helixorient(1)
