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21
Hi Di,

Thanks for the detailed response. I can only wish that all users are just like you in providing such helpful feedback. Over the years, it is users like you who have motivated me to keep working on DSSR ...

Best regards,

Xiang-Jun
22
RNA structures (DSSR) / Re: Can x3dna-dssr correctly handle N1-methyl-pseudouridine?
« Last post by Di_Liu on April 22, 2025, 03:29:03 pm »
Hi Xiang-Jun,

Thank you for your detailed and insightful response. I'm truly impressed by your meticulous attention to details! It’s reassuring and strengthens my confidence in DSSR as a reliable tool!!! Also, thanks to your explanation and the referenced blog post, I now have a much clearer understanding of how the `--nt-mapping` option functions.​

I further tested `--nt-mapping`, and below is what I got:

Without `--nt-mapping`:
Code: [Select]
A.B8H7 has pseudo-uridine C1'...C5 glycosidic bond
B.B8H27 has pseudo-uridine C1'...C5 glycosidic bond

With `--nt-mapping='B8H:p'`, the result is the same as above, and the message reads:
Code: [Select]
uncommon base 'B8H' assigned to 'p' for A.B8H.7
uncommon base 'B8H' assigned to 'p' for B.B8H.27
A.B8H7 has pseudo-uridine C1'...C5 glycosidic bond
B.B8H27 has pseudo-uridine C1'...C5 glycosidic bond

With `--nt-mapping='B8H:u'`, I'm intentionally confusing the software to treat it as uridine, and I got the warning:
Code: [Select]
uncommon base 'B8H' assigned to 'u' for A.B8H.7
uncommon base 'B8H' assigned to 'u' for B.B8H.27
A.B8H7 has unusual GLYCOSIDIC bond!
B.B8H27 has unusual GLYCOSIDIC bond!

Best regards,

Di
23
General discussions (Q&As) / MOVED: Rebuilding circular Z-DNA
« Last post by xiangjun on April 22, 2025, 12:14:22 pm »
24
RNA structures (DSSR) / Re: Rebuilding circular Z-DNA
« Last post by xiangjun on April 22, 2025, 12:13:54 pm »
Hi Di,

Thanks for chiming in on the topic on modeling Z-DNA structures with proper backbones. User @shr "would also look forward to Z-DNA backbones being included in DSSR modeling functionalities."

Let's continue the discussion through this thread. Your special interest in circular Z-DNA structures will also be taken into account.

In addition to splitting the topic as a new thread, I have also moved the thread under the Section on RNA structures (DSSR) from "General discussions (Q&As)". I aim to develop this feature within DSSR. As noted previously, the classic 3DNA suite of programs has been superseded by DSSR.

If you and @shr could share what you have done so far, I would very much like to see. The more concrete examples, the better.

Best regards,

Xiang-Jun
25
Hi Di,

As a follow-up to my previous response to your question, I have just written up a blog post on this topic: See Mapping of modified nucleotides in DSSR. In particular, from the listed ANSI C code, you should find the answer on how DSSR uses atomic connectivity to decide on pseudouridine modifications.

Best regards,

Xiang-Jun
26
General discussions (Q&As) / Re: Rebuilding Z-DNA
« Last post by xiangjun on April 22, 2025, 09:57:23 am »
Quote
Apologies for it took a while to reply. Thank you for your help with the structure! I used phenix to minimise like you suggested and I can use it for my analysis now.

Thanks for the confirmation that the DSSR modeled Z-DNA structure works for your case. It is through interactions with real-world users like you that makes DSSR relevant and useful.

Even though virtual, a forum thread is just like a conversation. I strive to respond to users' questions timely and concretely. Users who initiate a thread are expected to follow up with their progress and share their findings, or the lack thereof. It’s a two-way street, and I appreciate your engagement and contributions to the forum.

As a follow up, I am planing to write a blogpost to summarize the discussion and provide step-by-step details on how the extended Z-DNA structure was built using DSSR. This may take a couple of days, and I will provide a link here once it is ready.

Quote
I would also look forward to Z-DNA backbones being included in DSSR modeling functionalities.

I have split a new thread titled "Rebuilding circular Z-DNA". Please share your thoughts and suggestions on this topic over there.

Best regards.

Xiang-Jun

27
Hi Di,

Thanks for your well formulated question regarding x3dna-dssr’s support of N1-methyl-pseudouridine, B8H.

Quote
I understand that x3dna-dssr can handle pseudouridine (PDB Chem ID: PSU) correctly. I'm inquiring about its support for N1-methyl-pseudouridine (PDB Chem ID: B8H). Specifically,​ does x3dna-dssr recognize B8H based on its PDB chemical ID, or does it rely on atomic connectivity?

FYI, I've tested x3dna-dssr with PDB entries 8PFK and 8PFQ, both containing B8H, and the analysis proceeded without errors, with the results looking reasonable. However, given the unique C5-C1′ glycosidic bond for B8H, I want to confirm that x3dna-dssr interprets this modification accurately.

DSSR uses atomic connectivity to identify pseudouridine or its modified forms, including B8H. DSSR User Manual contains the following relevant information:

Quote
Note that pseudouridine, the most prevalently modified nt in RNA, is denoted P† in DSSR and the small case p is reserved for potential modified pseudouridines. ... footnote: †Not to be confused with the phosphorus atom in the backbone phosphate group. The distinction should be clear in context.

While anticipated, your reported case of B8H is the first time I see a modified pseudouridine. In DSSR output for 8PFK, you will see the following:

Code: Text
  1. #x3dna-dssr -i=8PFK.pdb -o=8PFK.out
  2.  
  3. From 8PFK.out
  4. ****************************************************************************
  5. List of 1 type of 1 modified nucleotide
  6.       nt    count  list
  7.    1 B8H-p    1    A.B8H7
  8.  
  9. From dssr-torsions.txt
  10. 7     p A.B8H7 ... chi -155.3(anti)

The chi for B8H is defined using O4'--C1'--C5--C4 instead of O4'--C1'--N1--C2, which would make no sense for pseudouridine. This is a little detail that DSSR pays attention to where other tools may not. See my blogpost Torsion angles from DSSR. You could easily verify this, using PyMOL for example, to measure the torsion angle by clicking four atoms in order.

The DSSR results for 8PFQ are also as expected with correct identification of B8H as a modified pseudouridine.

Quote
Further, is there a comprehensive list of modified nucleotides currently supported by x3dna-dssr?​ I came across these two pages (https://x3dna.org/highlights/automatic-identification-of-nucleotides ; https://x3dna.org/highlights/modified-nucleotides-in-the-pdb ), but could not find the exact answer.

To answer your question, here is an excerpt from my recent response to a similar inquiry:

Quote
Over the years, I've refined the heuristics of the mapping process. In the early days with 3DNA, I kept an ever increasing list of 'baselist.dat' with hundreds of entries like: MIA   a that maps MIA as a modified A, denoted as lowercase 'a'. In the current DSSR, I keep only the standard ones, with 48 entries total (see attached DSSR-baselist.txt). If a residue is not a standard one, the following function is called to do the mapping (DSSR performs filtering to decide if it is a nucleotide, and if so R or Y). DSSR also has a command-line option --nt-mapping as documented in the screenshot.

The DSSR-baselist.txt is attached for your reference. I am planning to write blogpost with details on this topic.

Best regards,

Xiang-Jun

28
RNA structures (DSSR) / Can x3dna-dssr correctly handle N1-methyl-pseudouridine?
« Last post by Di_Liu on April 22, 2025, 12:48:13 am »
Hi Xiang-Jun,

I understand that x3dna-dssr can handle pseudouridine (PDB Chem ID: PSU) correctly. I'm inquiring about its support for N1-methyl-pseudouridine (PDB Chem ID: B8H). Specifically,​ does x3dna-dssr recognize B8H based on its PDB chemical ID, or does it rely on atomic connectivity?

FYI, I've tested x3dna-dssr with PDB entries 8PFK and 8PFQ, both containing B8H, and the analysis proceeded without errors, with the results looking reasonable. However, given the unique C5-C1′ glycosidic bond for B8H, I want to confirm that x3dna-dssr interprets this modification accurately.

Further, is there a comprehensive list of modified nucleotides currently supported by x3dna-dssr?​ I came across these two pages (https://x3dna.org/highlights/automatic-identification-of-nucleotides ; https://x3dna.org/highlights/modified-nucleotides-in-the-pdb ), but could not find the exact answer.

Thank you for your assistance!
29
General discussions (Q&As) / Re: Rebuilding Z-DNA
« Last post by shr on April 21, 2025, 11:22:48 pm »
Apologies for it took a while to reply. Thank you for your help with the structure! I used phenix to minimise like you suggested and I can use it for my analysis now. I would also look forward to Z-DNA backbones being included in DSSR modeling functionalities.
30
RNA structures (DSSR) / Rebuilding circular Z-DNA
« Last post by Di_Liu on April 21, 2025, 08:10:12 pm »
Hi Xiang-Jun, I think three steps are needed for creating such a Z-DNA ring or more generally, any Z-form helical structures:

(1) Obtaining a helical parameter file in a similar way as the A- or B-form helices;
(2) Creating the atoms of the bases based on the helical parameter file;
(3) Putting the other atoms of the sugar and phosphate groups based on the position of the bases' atoms (there are only two conformations corresponding to the pyrimidines and purines, respectively).

Do you prefer that I start a new thread on this topic?

Thanks!
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Funded by the NIH R24GM153869 grant on X3DNA-DSSR, an NIGMS National Resource for Structural Bioinformatics of Nucleic Acids

Created and maintained by Dr. Xiang-Jun Lu, Department of Biological Sciences, Columbia University