g_helixorient

Main Table of Contents

VERSION 4.5
Thu 26 Aug 2010


Description

g_helixorient calculates the coordinates and direction of the average axis inside an alpha helix, and the direction/vectors of both the alpha carbon and (optionally) a sidechain atom relative to the axis.

As input, you need to specify an index group with alpha carbon atoms corresponding 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/CA-vector as Y, and the Z axis from their cross product. We use the Euler Y-Z-X rotation, meaning we first tilt the helix axis (1) around and (2) orthogonal 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 theta1-3.xvg

Files

optionfilenametypedescription
-s topol.tpr Input Run input file: tpr tpb tpa
-f traj.xtc Input Trajectory: xtc trr trj gro g96 pdb cpt
-n index.ndx Input, Opt. Index file
-oaxis helixaxis.dat Output Generic data file
-ocenter center.dat Output Generic data file
-orise rise.xvg Output xvgr/xmgr file
-oradius radius.xvg Output xvgr/xmgr file
-otwist twist.xvg Output xvgr/xmgr file
-obending bending.xvg Output xvgr/xmgr file
-otilt tilt.xvg Output xvgr/xmgr file
-orot rotation.xvg Output xvgr/xmgr file

Other options

optiontypedefaultdescription
-[no]h gmx_bool no Print help info and quit
-[no]version gmx_bool no Print version info and quit
-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 or none
-[no]sidechain gmx_bool no Calculate sidechain directions relative to helix axis too.
-[no]incremental gmx_bool no Calculate incremental rather than total rotation/tilt.


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