<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class=""><div class=""></div><div class=""><br class=""></div><div class=""><br class=""></div><div><blockquote type="cite" class=""><div class="">On 10 Apr 2017, at 20:30, Eric Pettersen <<a href="mailto:pett@cgl.ucsf.edu" class="">pett@cgl.ucsf.edu</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><meta http-equiv="Content-Type" content="text/html charset=utf-8" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">Hi George,<div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>Mathematically, radius of gyration is pretty simple. From Wikipedia: radius of gyration is the root mean square distance of the object's parts from its center of mass. Looking at the script, perhaps the radius of gyration computation should not be mass weighted. The script I’ve attached eliminates that mass weighting. Let me know if that gives the results you expect.</div><div class=""><br class=""></div><div class="">—Eric</div><div class=""><br class=""><div class="">
<div style="letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>Eric Pettersen</div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>UCSF Computer Graphics Lab</div><div class=""><br class=""></div></div></div></div></div><span id="cid:5F900BA3-0167-4AAE-A392-592589D22470"><radius-of-gyration.py></span><meta http-equiv="Content-Type" content="text/html charset=utf-8" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class=""><div class=""><br class="Apple-interchange-newline"><br class="Apple-interchange-newline">
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<br class=""><div class=""><blockquote type="cite" class=""><div class="">On Apr 7, 2017, at 11:16 AM, George Tzotzos <<a href="mailto:gtzotzos@me.com" class="">gtzotzos@me.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class="">Hi Elaine,<br class=""><br class="">The reason I asked is because I’ve measured the radius of gyration of a particular ligand during the course of an MD trajectory using AmberTools. Comparing the mean radius of gyration of the ligand during the trajectory with the corresponding value generated by the Chimera script, the difference is by a factor of 4. AmberTools radius of gyration is also in angstrom.<br class=""><br class="">Have a good day<br class=""><br class="">George<br class=""><br class=""><blockquote type="cite" class="">On 7 Apr 2017, at 19:58, Elaine Meng <<a href="mailto:meng@cgl.ucsf.edu" class="">meng@cgl.ucsf.edu</a>> wrote:<br class=""><br class="">Hi George,<br class="">Units would be the same as your atomic structure coordinates, so yes, angstroms if you are just using “regular” PDB files. I’m not sure why you would expect different units.<br class="">Best,<br class="">Elaine<br class=""><br class=""><blockquote type="cite" class="">On Apr 7, 2017, at 10:48 AM, George Tzotzos <<a href="mailto:gtzotzos@me.com" class="">gtzotzos@me.com</a>> wrote:<br class=""><br class="">Thank you Eric,<br class=""><br class="">The problem was exactly what you identified. I assume the units are in Angstrom<br class=""><br class="">George<br class=""><br class=""><blockquote type="cite" class="">On 7 Apr 2017, at 01:46, Eric Pettersen <<a href="mailto:pett@cgl.ucsf.edu" class="">pett@cgl.ucsf.edu</a>> wrote:<br class=""><br class="">Hi George,<br class=""><span class="Apple-tab-span" style="white-space:pre"> </span>First, that script measures the radius of gyration for all the atoms in a model, not just ligands atoms or some subset of the model’s atoms. So, my best guess is that the model that’s from your MD simulation has a lot solvent atoms that Chimera isn’t displaying by default. So you should check that there are the same number of atoms in both models. One way to do that is with the command:<br class=""><br class="">sel #0 (number of selected atoms [all of model 0] shown in the status line)<br class="">sel #1 (same thing for model 1).<br class=""><br class=""><span class="Apple-tab-span" style="white-space:pre"> </span>If the difference in the models is the solvent you would want to use the command “delete solvent” before running the gyration script.<br class=""><br class="">—Eric<br class=""><br class=""><br class=""><span class="Apple-tab-span" style="white-space:pre"> </span>Eric Pettersen<br class=""><span class="Apple-tab-span" style="white-space:pre"> </span>UCSF Computer Graphics Lab<br class=""><br class=""><br class=""><blockquote type="cite" class="">On Apr 6, 2017, at 12:35 PM, George Tzotzos <<a href="mailto:gtzotzos@me.com" class="">gtzotzos@me.com</a>> wrote:<br class=""><br class="">Taking a reference PDBID 3n7h, I’ve generated for an MD simulation topology and restart files.<br class=""><br class="">I’ve loaded on Chimera 3n7h and then the starting frame of the MD simulation. <br class="">Used the MatchMaker and found perfect superposition of the protein backbone and two ligands (3n7h is #0 and the ligands #0:129.A and #0.132.B<br class=""><br class="">I run the radius of gyration script (see attached). I found that the radii of gyration for the ligands in the two models are completely different.<br class=""><br class="">#0 center of mass: 12.6543 10.4356 15.4086, radius of gyration: 21.182<br class="">#1 center of mass: 42.7381 42.5171 42.6163, radius of gyration: 37.390<br class=""><br class="">I don’t follow why this is so. Any explanation would be most welcome.<br class=""><br class="">A second question regards the units of the radii of gyration. Are they Angstrom or nm?<br class=""><br class="">Thank you in advance<br class=""><br class="">George<br class=""><br class=""><rad_gyration.py>_______________________________________________<br class="">Chimera-users mailing list: <a href="mailto:Chimera-users@cgl.ucsf.edu" class="">Chimera-users@cgl.ucsf.edu</a><br class="">Manage subscription: <a href="http://plato.cgl.ucsf.edu/mailman/listinfo/chimera-users" class="">http://plato.cgl.ucsf.edu/mailman/listinfo/chimera-users</a><br class=""></blockquote><br class=""></blockquote><br class="">_______________________________________________<br class="">Chimera-users mailing list: <a href="mailto:Chimera-users@cgl.ucsf.edu" class="">Chimera-users@cgl.ucsf.edu</a><br class="">Manage subscription: <a href="http://plato.cgl.ucsf.edu/mailman/listinfo/chimera-users" class="">http://plato.cgl.ucsf.edu/mailman/listinfo/chimera-users</a><br class=""></blockquote><br class=""></blockquote><br class=""><br class="">_______________________________________________<br class="">Chimera-users mailing list: <a href="mailto:Chimera-users@cgl.ucsf.edu" class="">Chimera-users@cgl.ucsf.edu</a><br class="">Manage subscription: <a href="http://plato.cgl.ucsf.edu/mailman/listinfo/chimera-users" class="">http://plato.cgl.ucsf.edu/mailman/listinfo/chimera-users</a><br class=""><br class=""></div></div></blockquote></div><br class=""></div></div></div></blockquote></div><br class=""></div></body></html>