From: Vermaas, Joshua (
Date: Wed Aug 03 2016 - 13:24:32 CDT

Hi Stephanie,

The way I like doing it is through two successive calls to pbctools.

pbc wrap -compound fragment -center com -centersel "chain A"

pbc wrap -compound fragment -center com -centersel "protein"

The idea behind these two commands is that the first will center is on one component of the protein. For most multimers, that will also put the other elements in the same box, and so you eliminate jumps that way. The second line then recenters it so that the protein as a whole is in the center of the box, not just one fragment. The second one could be replaced by another alignment script if you prefer.

-Josh Vermaas

On 08/03/2016 11:31 AM, kim, stephanie S. wrote:


I've tried to align a trajectory of a protein consisting two chains, but when I load the aligned version of the trajectory, two chains separate, jump around for couple of frames and then would come back. A colleague suggested using ptraj commands: "center" and "image center familiar" instead, because he had the same problem before with aligning a trajectory consisting two subunits using vmd.

Can you suggest any other tcl scripts that would fix this problem? Or could you suggest a script that correlates to the ptraj command "center" and "image center familiar"?

I've used this script to align the trajectory:


proc align { rmolid smolid2 seltext } {
  set ref [atomselect $rmolid $seltext frame 0]
  set sel [atomselect $smolid2 $seltext]
  set all [atomselect $smolid2 all]
  set n [molinfo $smolid2 get numframes]

  for { set i 1 } { $i < $n } { incr i } {
    $sel frame $i
    $all frame $i
    $all move [measure fit $sel $ref]
$ref delete
$all delete
$sel delete

align 0 0 "protein"


Thank you,

Stephanie Kim

Graduate Student

Department of Chemistry and Biochemistry

The Ohio State University

2116 Newman & Wolfrom Laboratory

100 W. 18th Ave
Columbus, OH 43210