[chimerax-users] hbonds and the number of detected interactions

[Elaine Meng]

There is a misunderstanding: please read the hbonds help, the link I sent before.  The "slop" values are not the cutoffs; instead they are used to expand the ranges of the cutoffs.  There is no single angle cutoff  or distance cutoff.  Instead, many different cutoffs are used for different combinations of atom types depending on their elements and hybridization states.  These multiple cutoff values are listed in several tables in a publication cited in the help page.  If you cannot access that publication let me know.

Also the default "slop" values are what we recommend for most PDB files.  If you increase the values very much, you may get very poor results, "bad" (or impossible) H-bonds.
Elaine


> On Jan 26, 2022, at 11:34 AM, Enrico Martinez <jmsstarlight at gmail.com> wrote:
> 
> p.s. I've just increased angle to 35 and the distance to 0.7: now
> there is contact with the Thr26 which is more distant, but not with
> the Glu which is on the line with the NH of the ligand .. I attached
> the picture :-)
> 
> ср, 26 янв. 2022 г. в 20:26, Enrico Martinez <jmsstarlight at gmail.com>:
>> 
>> Thanks a lot, Elaine!
>> may you specify abit more regarding distSlop option, the values in the
>> nm ? so 0,4 corresponds to 4 A, doesn't it? What the upper limit may
>> be reasonable?
>> Cheers,
>> Enrico
>> 
>> ср, 26 янв. 2022 г. в 18:48, Elaine Meng <meng at cgl.ucsf.edu>:
>>> 
>>> 
>>> 
>>>> On Jan 26, 2022, at 8:50 AM, Enrico Martinez via ChimeraX-users <chimerax-users at cgl.ucsf.edu> wrote:
>>>> 
>>>> Dear ChimeraX users!
>>>> I have a question regarding calculations of the hydrogen bonds and its
>>>> visualisation using hbonds. Here is my command:
>>>> hbonds #1 & ligand reveal true log true radius 0.06 dashes 6 color
>>>> turquoise distSlop 0.4 angleSlop 20 intraRes false
>>>> 
>>>> So I ignore intraRes (since the ligand is also present in the #1) and
>>>> calculate hydrogen bonds using default parameters.
>>>> 
>>>> 1) How can I modify geometric criteria for the calculations (is this
>>>> distSlop / angleSlop) to increase the distance for the consideration
>>>> of potential h-bonds ?  In particular as you may see on the attached
>>>> image the bond between the side-chain of the Glu166 and NH of the
>>>> ligand is absent (I've just checked the same structure using py*ol and
>>>> it could detect this contact).
>>> 
>>> Yes, angleSlop makes the angle criteria looser and distSlop makes the distance criteria looser.  Larger values = more permissive, meaning more tolerant of suboptimal H-bond geometry. These parameters are explained in the hbonds help:
>>> <https://rbvi.ucsf.edu/chimerax/docs/user/commands/hbonds.html>
>>> 
>>>> 2) In the case of another ligand, I could visualize two h-bonds
>>>> provided by two hydrogens of the side chain of the Gln189 (same
>>>> residue) with two different oxygens of the ligand. Is this correct?
>>> 
>>> Each possible H-bond is evaluated by itself, i.e. it is not necessarily true that all of the possible H-bonds that are found could be correct at the same time. The program will correctly use the distance and angle information it is given, but (just like almost anything in life) you should also pay attention and use your own judgment.  For example, sometimes it will find two H-bonds between the same two atoms if they could both be donor or acceptor (D->A and A<-D).  However, in the situation you mention I don't see any reason to think it is not correct. There are two hydrogens and they could certainly be pointing toward two different oxygens of the ligand.
>>> 
>>> I hope this helps,
>>> Elaine
>>> -----
>>> Elaine C. Meng, Ph.D.
>>> UCSF Chimera(X) team
>>> Department of Pharmaceutical Chemistry
>>> University of California, San Francisco
>>> 
> <hbond_tet.png>