Hydrogen bond shown only on one side of a Tetramer (and get 1 Buns for free!)

Case number:671071-2011798
Topic:Game: Other
Opened by:HuubR
Opened on:Friday, June 25, 2021 - 20:43
Last modified:Friday, June 25, 2021 - 20:43

In puzzle 2006, I noticed a strange situation: a Hydrogen Bond that is shown from segment 1 on Chain 1 to segment 9 on Chain 0, but not shown as its "mirror image", from segment 1 on Chain 0 to segment 9 on Chain 1.  And, even stranger: it leads directly into a blue Buns.

I found this when a Buns emerged in my solution, and I wanted to fix it by making a Hydrogen Bond.  To my surprise, that bond was already there!   It could be that I am missing something here, but in my mind, a Buried polar that makes a hydrogen bond cannot be UNSatisfied at the same time, so it cannot be a BUNS.

I made two almost identical views of the same situation, looking at two different corners of the Tetramer.  One view, with Chain 0 at the top and Chain 1 (purple) at the right hand side, shows two hydrogen bonds to the backbone of Chain 3 (brown, bottom left), as well as one Buns on the N terminus (segment 1: the yellow one).  That could make sense, although one of the acceptors of the purple segment 9 (in the middle of the picture) seems to be in an ideal position for a hydrogen bond.

Segment 1 showing two H-Bonds to the left
This view DOES show the H-Bond to the right

The second view shows another corner of the Tetramer.  This view has Chain 0 at the right hand side and Chain 1 (purple) at the top.  The two bonds from segment 1 to the left are not shown in this view, because in this corner they go from Chain 1 (purple) to Chain 2 (green).  But the bond to the right, that was not shown in the other view, is now shown, together with the Buns!

Around the time this puzzle closed, I have uploaded a similar solution for scientists (Puzzle 2006, 22155 points), showing the same phenomenon.

I have no idea how often a situation like this occurs.  There are a couple of specific circumstances that might play a role here:

  • It is a hydrogen bond between backbone (donor side) and sidechain (acceptor), which is not very common.
  • The donor side is the N terminus, which means that this Amino group has three Hydrogens (all other residues have only one H in the Amino group).  In my example, all three of them make H-Bonds.  That is probably even less common.

I do not think this bug (if it is one indeed) should get a high priority to be fixed.  But I would like to know whether it is indeed a bug, or I have simply misunderstood something here.

(Fri, 06/25/2021 - 20:43  |  0 comments)


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