[Chimera-users] Basic question re: nucleotide sequence

[Elaine Meng]

Hello Chad,
Chimera does not translate nucleic acid sequence into amino acid sequence, nor does it do “de novo” (without a template 3D structure) modeling, sorry.

There are a lot of translation tools online… googling finds these and several more:
<https://web.expasy.org/translate/>
<http://www.bioinformatics.org/sms2/translate.html>
<http://insilico.ehu.es/translate/>

Comparative modeling requires a related 3D structure, which might even have relatively low sequence identity with your structure of interest.  In general, the reliability of the sequence alignment between the two and of the resulting 3D model will be lower for lesser sequence identity.  You could try using the Modeller approach available in Chimera if you can find known structures that might be sufficiently related.  Usually this is done with BLAST search for similar sequences in the PDB, or threading your sequence of interest through known 3D structures.  

Chimera can do BLAST vs. PDB either in the Blast Protein tool (menu: Tools… Sequence.. Blast Protein) or “mda” command to find template(s), followed by use of Modeller comparative modeling with known template(s)
<http://www.rbvi.ucsf.edu/chimera/docs/UsersGuide/blast.html>
<http://www.rbvi.ucsf.edu/chimera/docs/UsersGuide/midas/mda.html>

For example, if I use “mda” on Uniprot Q6F9H7 it finds me 4 templates with 43-47% sequence identity with the query (as does Blast Protein, but then it takes more steps to see the % identity).

… but for threading, or completely de novo modeling, you would need to use some other software outside of Chimera.  You could also see if there’s already models for your sequence in ModBase, but these are also comparative models (based on alignments with known structures) built with Modeller.
<https://modbase.compbio.ucsf.edu/modbase-cgi/index.cgi>

Best,
Elaine
-----
Elaine C. Meng, Ph.D.
UCSF Chimera(X) team
Department of Pharmaceutical Chemistry
University of California, San Francisco

> On Nov 24, 2018, at 4:57 PM, Pecot, Chad V. <pecot at email.unc.edu> wrote:
> 
> Hello,
> I am trying to use Chimera to predict the structure of a nucleotide sequence that does not have a PDB ID. This is an unstudied protein, and I’m hoping to get some structure information and to visualize it using the software.
>  
> I tried using the tutorials, but the best I can tell it appears to work off of already available PDB IDs.
>  
> Is there a way I can enter the nucleotide sequences as a starting point? If so I’d really appreciate a few step/steps on how to do this. 
> Best,
> Chad