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<div class="">Thank you, Dorothee & Henry for the very informative articles. I agree that their occupancies don’t have to add up to unity since they’re separate entities. </div>
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<div class="">I’d encountered scenario 7 before with two doubly disordered side chains with one conformer each sharing the same space. The altloc and constrained group occupancies combination worked just as described. However, this time, a different protein,
with a ligand and a side chain sharing the same space, group occupancy constraints do not work. The ligand and the PHE residue each has just a single conformation as far as I can tell. When the ligand is bound, the PHE side chain must be out, thus the PHE
must have at least two conformations for this to be physically possible. I followed the protocol in the News Letter, created an alternative conformation for the phenylanine in question and constrained the group occupancies accordingly:</div>
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<div style="margin: 0px; line-height: normal;" class=""><span style="font-size: 12px;" class="">refinement {</span></div>
<div style="margin: 0px; line-height: normal;" class=""><span style="font-size: 12px;" class=""> refine {</span></div>
<div style="margin: 0px; line-height: normal;" class=""><span style="font-size: 12px;" class=""> occupancies {</span></div>
<div style="margin: 0px; line-height: normal;" class=""><span style="font-size: 12px;" class=""> constrained_group {</span></div>
<div style="margin: 0px; line-height: normal;" class=""><span style="font-size: 12px;" class=""> selection = resname LIG or (chain B and resseq 890 and altloc A)</span></div>
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<div class="">The ligand and APHE got pushed away from one another and off of their respective densities. Occupancies for both were reduced to 0.5 for the refinement. What am I doing wrong here? Does the ligand need to have an altloc as well? But I don’t see
an alternative conformation. </div>
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<div class="">Thanks,</div>
<div class="">Jason</div>
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<div class="">On Feb 28, 2018, at 5:35 PM, van den Bedem, Henry <<a href="mailto:vdbedem@slac.stanford.edu" class="">vdbedem@slac.stanford.edu</a>> wrote:</div>
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If the phe is a gatekeeper, shouldn’t the ligand be refined at partial occupancy; i.e. occupancies not necessarily have to ‘add up’ as you suggest? Maybe this link is helpful too:<span class="Apple-converted-space"> </span><a href="http://www.biorxiv.org/content/early/2018/01/24/253419" style="color: rgb(149, 79, 114); text-decoration: underline;" class="">www.biorxiv.org/content/early/2018/01/24/253419</a><o:p class=""></o:p></div>
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H<o:p class=""></o:p></div>
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<b class=""><span style="font-size: 12pt;" class="">From:<span class="Apple-converted-space"> </span></span></b><span style="font-size: 12pt;" class=""><<a href="mailto:phenixbb-bounces@phenix-online.org" style="color: rgb(149, 79, 114); text-decoration: underline;" class="">phenixbb-bounces@phenix-online.org</a>>
on behalf of "Phan, Jason" <<a href="mailto:jason.phan@vanderbilt.edu" style="color: rgb(149, 79, 114); text-decoration: underline;" class="">jason.phan@vanderbilt.edu</a>><br class="">
<b class="">Date:<span class="Apple-converted-space"> </span></b>Wednesday, February 28, 2018 at 1:30 PM<br class="">
<b class="">To:<span class="Apple-converted-space"> </span></b>"<a href="mailto:phenixbb@phenix-online.org" style="color: rgb(149, 79, 114); text-decoration: underline;" class="">phenixbb@phenix-online.org</a>" <<a href="mailto:phenixbb@phenix-online.org" style="color: rgb(149, 79, 114); text-decoration: underline;" class="">phenixbb@phenix-online.org</a>><br class="">
<b class="">Subject:<span class="Apple-converted-space"> </span></b>[phenixbb] Overlapping ligand-protein side chain density<o:p class=""></o:p></span></div>
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<a name="_MailOriginalBody" class="">All, <span class="Apple-converted-space"> </span><o:p class=""></o:p></a></div>
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<span class="">A piece of a ligand and the side chain of a “gate-keeper” Phe occupy the same space with well-defined features observed for both (resolution is 1.7 A). It looks about 50:50. How do you refine both ligand and protein side chain in this case? A
couple of phenixbb suggestions for dealing with ligand-ligand overlapping density have been considered. With the first suggestion, the two entities still clashed and moved apart off of their respective densities. The second suggestion is not applicable in
this case since the other molecule is not a ligand but part of the protein but it was tested anyway. Although there was no bumping, the occupancies don’t add up, resulting in a big blob of negative density around the ligand piece. <o:p class=""></o:p></span></div>
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<span class="">Only two comments:<o:p class=""></o:p></span></div>
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<span class="">At that resolution, constrained group occupancy refinement should work reasonably well (provided you can model the 2 entities). Then you also do not have clashes between the molecules, because Occ(A)+Occ(B)=1, meaning when one (A) is there, the
other one (B) is not. This works with refmac (external keyword file); if you need more sophisticated occupancy re/constraints SHELXL may offer more opportunities.<o:p class=""></o:p></span></li><li class="MsoNormal" style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;">
<span class="">There is no necessity for the two NCS copies of the binding site to look exactly the same (non-equivalent). Maybe there is a good reason/story (accessibility, contacts etc) for one site to be occupied differently than the other one. <o:p class=""></o:p></span></li></ol>
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<span class="">Best, BR<o:p class=""></o:p></span></div>
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<span class="">——————————————<o:p class=""></o:p></span></div>
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<span class=""><span style="font-size: 10.5pt; font-family: Helvetica;" class="">Modeling two molecules that occupy overlapping binding sites in a structure simply involves designating them as alternate conformers, with the same chain and residue number, and
an occupancy that sums to 1.0. For example, if you have an AMP and an ADP that occupy the same binding site, you would define them as<o:p class=""></o:p></span></span></div>
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<span class=""><span style="font-size: 10.5pt; font-family: Courier;" class="">AAMP B 501</span></span><span class=""><span style="font-size: 10.5pt; font-family: Helvetica;" class=""><o:p class=""></o:p></span></span></div>
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<span class=""><span style="font-size: 10.5pt; font-family: Courier;" class="">BADP B 501</span></span><span class=""><span style="font-size: 10.5pt; font-family: Helvetica;" class=""><o:p class=""></o:p></span></span></div>
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<span class=""><span style="font-size: 10.5pt; font-family: Helvetica;" class="">and initially set the occupancies for the atoms in each conformer to the ratio (50:50, 30:70, etc.) that you observe in the density.<o:p class=""></o:p></span></span></div>
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<span class=""><span style="font-size: 10.5pt; font-family: Helvetica;" class="">Refinement in this manner is straightforward in PHENIX.<o:p class=""></o:p></span></span></div>
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<span class=""><span style="font-size: 10.5pt; font-family: Helvetica;" class="">Diana<o:p class=""></o:p></span></span></div>
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